When you are in the Mail app, move your mouse pointer to one of the right corners (top or bottom) and let the Charms Bar
appear. Alternatively, you can also press Windows + C.
Now, click on Settings and in the next screen click on Accounts. There, you will see a list which includes among others Hotmail and Gmail. Click on the relevant type and enter your details. Voila! Your accounts are configured.
I'm unable to provide screenshots now as I'm not logged into Windows, so use this source if you want visual help. http://winsupersite.com/article/windows8/windows-8-tip-adding-accounts-mail-app-143395