ie. how it works, contact us, team, about, press, terms, FAQ, hiring
An email login is generally best to start with unless your app will have tight integration with services like Facebook or Twitter, in which case social login is better.
This means you'll need to make an API (or Application Programming Interface). It's how all your friendly apps talk to each other.
A profile means that some of the people that use your app will have to enter information about themselves that might be viewed publicly.