What does the number in parentheses next to you mail icon mean?

Thank you for your time!

That number means how much unread mail you have. So if you have the number 3, it means you have 3 unread mail. If you read them/open them, the number will disappear.

hmm, mine says (0,14)?

This means you have 14 game mail notifications, to access your notifications from the game, click this button

Ooooh! I didn't see the folders lol Thank you both!!!

just a little add on to ET's comment, the order in the parenthesis is (inbox, game mail)

Ohh, that makes sense! Thank you! :D