You can have the role of a coach, a player or both. You need to select one type during registration. If you want to be able to log in with a different account type, go to Account Settings and add a new account type under My accounts.
Each account type has different permissions. Coaches have more privileges than players. It is worth mentioning that each account might have access to different teams. Having both account types and being a coach in a team doesn't make you a player in that team.