Actually Push Mail Alert is very simple:

  1. When you open it, you have 1 possible action: "Add account ...".
  2. This lead to one screen with only one possible action: Selection of your mail provider. Pick the one that match
  3. Enter your mail credential and save.

That's it !

Note: Push Mail Alert is only made for alerting. It does not download the mail or display you the content. All it does is send you push notifications.