How does the challenge feature work?

I created a ladder for users and i can’t submit a challenge. How do i schedule a match against another ladder user? Usually the challenge button is located in the user profile page or standings.

I need to know the members’ PSN or XBOX Live ID, What can i do about the registration page? I know i can add custom field but how will i know if the PSN/XBOX ID are valid?

When creating a tournament how can i change the “Game Format”
The tournament should display the username of the member who created the cup/league or ladder.