Assuming that it has been a straight migration from 2010 to 2013 all the old sites/teamrooms and associated permissions will still be there.
You could try manually entering the URL into the address bar in your browser. Alternatively, if you click the "sites" link at the top of the SharePoint page to the left of your name it lists all the sites you have access to.
If it is a fresh installation it is perfectly possible that the permissions and access rights to the sites have not been set up. If that is the case you will probably need to contact your SharePoint administrator.