You can sign in with your existing Google, Twitter, FaceBook, or Microsoft account, or create a new account.
NewsBrain gets articles from Feedly, then predicts your interest in them and shows the most interesting ones to you. Feedly scans millions of sites on the Internet to catalog its articles, and also keeps track of which articles you've already seen.
Once you've done the authorization, NewsBrain remembers it and uses it from then on. You shouldn't have to do it again unless the account somehow becomes invalid, or you restore your device, or delete and then re-download the NewsBrain app. To log out or change accounts, can get to this screen from the My Account item on the Source Screen for the Feedly source.