In order to enable Push Notifications you need to do the following:
1) create a Apple Push Notification Certificate (follow this tutorial http://support.brickandmobile.com/hc/en-us/articles/203657280-How-to-generate-an-APN-Certificate-cer-file-in-order-to-enable-Push-Notification-).
2) Go to Your app Dashboard by clicking [My Applications] on the top of any page and then clicking [Dashboard] near your app name.
3) Then click [Push Notifications]
4) Then upload the Push Notification Certificate using the form below
PS. The process is basically the same as for your Distribution certificate but you do it on another screen.