The company specifically names Yahoo and Hotmail/Outlook, so your AOL email (who are you?) won’t work with Gmail. But, you will be able to get all the goodness that comes with an official @gmail email address, like inbox filtering, spam blocking and even Google Now cards (for Android users).
Taking advantage of those features is called ‘Gmailify,’ and is an option in Gmail you’ll see when you log in using an alternative email. If you just want to use Gmail as an email client for your Yahoo or Hotmail/Outlook emails, you can turn Gmailify off.
Google is planning to roll the feature out to more email accounts in the future, so if you’re not on the list (AOL users, I’m looking at you) — don’t worry.