First time you use the application you have to sign up, by
1) clicking the "Sign in with Google+"-button and the application can use your existing Google password and user-name
2) clicking 'sign up!' and then putting in your name, email address and make own password
The advantage of the first approach (1) is that it will decrease the amount of username and passwords you need to know, as it uses something you already have. It is also faster.
With approach 2) you will come to this picture:
All users have to accept the Terms of service to procede