I am using MoCA very successfully in my home. I'm very happy with it. Running Cat-something would have made me happier, but was not practical to do.
You need a MoCA modem (also called a MoCA adapter) for each place where there's a coax cable and you want to plug in an Ethernet cable. This modem handles the "bridging" between Ethernet and the MoCA signal. What you plug into the MoCA modem can be an Ethernet switch or a wireless access point, so you can have a bunch of stuff using one modem.
Generally you would have only one cable modem installed, unless you have two accounts with your cable ISP (it's generally one cable modem per account). One MoCA modem will hook up at the place where the cable modem and your router are. Other MoCA modems can be installed wherever the cable TV line is. It doesn't interfere with cable TV either. MoCA actually uses a technology similar to cable internet, but in a much higher range of frequencies. The cable companies' outside plants don't generally carry these but most people's inside wiring can.
You will want a wireless router that also does routing to wired stations. i.e. it needs to have Ethernet jacks for the inside network. Using a separate router and wireless access point will also work.
My MoCA modems are made by Motorola. I found them used on eBay for around $40 each. Other manufacturers I know of are Actiontec and Netgear. All MoCA hardware regardless of manufacturer should be interoperable.
The diagram here is a slightly-more-elaborate version of the one I made for myself when I did my setup. (Please forgive the crudity of this model; I didn't have time to build it to scale or to paint it...)
Black lines are cable TV cable (preferably RG6), orange lines are Ethernet.
"NIM100" is the model of the Motorola modems I happen to be using. I left the model number there because this is the only modem model I've actually used, and this diagram might not work for other types. i.e. this is not a product recommendation, just a qualification that this diagram may be specific to the Motorola Network Interface Module model 100. (I hope this avoids unwanted attention from the "product recommendation" police.) But from what I could tell from a quick look at a couple of other manufacturers' installation guides, they all get hooked up the same way.
UPDATE: Since writing this I've upgraded to Actiontec "Bonded MoCA 2.0 Network Adapters", which give 1 Gbps throughput. They hook up the exact same way as the NIM100's.
COAX connections
OUT vs IN
The weird thing about MoCA modems is the terminology on the cable jacks. For the modem that is near your cable modem, i.e. where your cable comes in, "cable out" means "this jack receives cable company's signal from the OUTside cable". This connection is necessary if you want your indoor cable system to carry cable TV signals, as it presumably does now.
For all others, "cable out" means "this jack provides signal that originally came from the OUTside cable." i.e. "cable out" means "outside cable signal", not necessarily "signal generated by this box." In the case of the box in the first room shown here it is very definitely not "signal output from this box". (Well, there is a little, but we have to block it, as I'll describe.)
In other words all of the "out" jacks on the MoCA modems are, in effect, connected together (as if they were all "out" jacks on a cable TV splitter), and they are how your cable company's signal gets through the system to the TVs and so on in your house. In my diagram, it's via the "cable out" jacks that cable TV channels coming from the cable TV OUTside plant (shown in the upper left corner) are getting to the "TV set or cable box" (shown in the third room).
You connect all of the MoCA boxes' "IN" coax jacks to your INside cable wiring.
Cable Splitters
If you have more than two rooms (counting the one where the cable comes in, and the first one "downstream"... i.e. the top two of the three on the diagram) the cable from the "In" jack on the first MoCA modem will have to go through one or more splitters, just as it would if it went to multiple TVs.
The best way to do this would be a single n-way splitter connected to the CABLE IN jack of th first MoCA modem, and a separate cable run to each of the n other rooms. This is called a "home run" arrangement in CATV jargon, but a less industry-specific term would be "star configuration". In many buildings though the cable is just run serially from one room to the next; if you take a wall plate off you'll usually find a two-way splitter, with one leg feeding the room's cable and the other feeding further downstream.
Or you might find just two coax with a barrel connector between them, in which case you'll have to buy and add a splitter. It may take some experimenting to figure out which of the two cables is the "upstream" (goes back to the cable entry point) and the "downstream" lead.
In this "daisy chain" configuration each room the cable passes except the last would have a 1:2 splitter wired this way, each "downstream" cable being fed with half the signal that came from the "upstream". Since splitters split the signal about in half this means the room with the first splitter gets 1/2 of the original signal strength, the next gets 1/4, etc. This isn't ideal. "Star" configuration is much better. If you have four rooms they all get about 1/4 the signal strength, which you may be able to boost to allow for the losses.
In my experience you can split the inside cable about as many ways as you could if the first MoCA modem wasn't there. i.e. if you already have cable jacks where you need them, and they are already carrying the cable TV signal, there are splitters somewhere and you should be able to use those cables and the splitters as is.
One potential problem: The splitters have to be able to pass signals bidirectionally, and they also have to be good to 2 GHz. Most modern splitters will work, but if you have to buy splitters, be sure they meet these specs. Best of all is if you can find splitters marketed for use with MoCA.
Other cable nuances
There are two other possibly-unfamiliar things to point out in the diagram.
The first is the box labeled "POE filter". POE here stands for "point of entry". It stops MoCA-band signals from getting out of your house and into the cable system's outside plant. It's recommended for any MoCA installation. Google "MoCA POE filter", you'll find many of them offered. They should cost less than $10.
The other thing to point out is the home plate-shaped thing labeled "T", connected to the "cable out" jack on the MoCA modem in the second (middle) room. "T" here stands for "terminator". You need one on any cable TV connector in the system, such as unused outputs on splitters, that isn't connected to anything else. (This is true even if you have no MoCA devices at all!)
Terminators maintain the correct impedance through your inside wiring, avoid "signal reflections", and prevent the cable or MoCA signals from "leaking" out of unterminated connectors. All of the above can be serious problems.
Terminators look like cable TV "F" connectors but with no cable coming out the back end. They should cost well under $5 apiece. Some splitters come with them; you're supposed to use one on every output that is otherwise unused. And you should.
Connecting TVs, etc.
If you also want a TV or cable box in a room with a MoCA modem, you connect it to the MoCA box's "cable out" jack. (And, I will state again: If you don't have a TV or cable box in a room with a MoCA modem, you really should have a terminator on that modem's "cable out" jack.)
I'm not sure whether MoCA modems support the bidirectional communication needed for e.g. the pay-per-view services on some cable systems. (The same bugaboo that has afflicted CableCard.) They should, since after all they pass signals from their "out" to their "in" jack.
Ethernet connections
The thing to remember is that the MoCA modems give you the functional equivalent of an Ethernet switch somewhere in the walls with an outlet jack in each room. Whatever you could do with that setup, you can do with this.
In the first room
So, cable TV signals come into your first room. We go through a splitter that sends the signal both to your inside cable network (via the MoCA modem) and to your cable modem. Your cable modem does the usual job of providing IP communications over Ethernet and maybe WiFi.
My diagram assumes that you have a separate WiFi router in that first room. Ethernet from your cable modem (which has not been "routed", it's using the IP address your ISP gave you) goes to your router's WAN jack as usual. The routers' LAN jacks then provide "routed" Ethernet just like your wireless does, usually using IPs 192.168.x.x.
You connect 0ne of the router's LAN jacks to the Ethernet jack on the first MoCA modem. That modem modulates the Ethernet signal (see, it is a modem!) onto a high frequency carrier, mixes this signal with the cable company's signal, and puts the whole on your inside cable wiring.
I've never seen an example of a cable modem that had the MoCA functionality in the same unit, but it's certainly possible. If it did, it would have two coax connectors, one "out" to connect to the feed from the outside cable, one "in" to connect to your inside coax, and you wouldn't need the splitter in the first room. And it would likely have two Ethernet jacks, one labeled "WAN" and the other "LAN". You would connect the latter to the "WAN" side of your router and the other to the "LAN" side. The latter is what would be bridged to your interior cable wiring.
You could even have a wireless router in the same box - then you would not have the "WAN" jack, but hopefully there would be several "LAN" jacks.
In other rooms
Now, wherever you want Ethernet, you connect the cable coming into that room to the "in" jack of a MoCA modem. Its Ethernet jack can go directly to a computer, or to an Ethernet switch if you have a bunch of wired devices, or...
...or to a wireless router. (If it's a switch, it will not have "WAN" or "LAN" jacks, just a bunch of jacks.) Important: Unless you want the various rooms on separate subnets or something, you must configure this wireless router in access-point-only mode. For most routers that just means the Ethernet comes into the router's LAN jack, not WAN. This is because you (usually) don't want cascaded routers. You could also use a wireless access point here, which would just have a single Ethernet jack and no option to do routing.
If you do want different subnets or some such in the various rooms... that's more about TCP/IP configuration than it is about MoCA; I'm not going to cover that.
Hope this helps!