About Those Roles
Your team members can be Players, Guests, or Non-Players.
Players are always invited to all games and events. If you don't have enough players for an activity, you will get an alert email before the game. Most of your people should be players.
Guests (aka backups) are only invited if you manually request them. To invite guests, hit the "Invite Guests" button on the activity page, below the list of guests.
Teams use the Guest role to have a group of backup players they can call on when they are looking short; also some teams use the Guest role to invite try-out players to selected events e.g. training or a scrimmage.
Non-Players don't receive invites (*). This role is intended for long-term absentees (e.g. players who are injured or otherwise absent for a period of time) who won't find invitations useful, or for admin staff who also don't need to see invitations. Non-players can still visit the website to see the team schedule, though, and sync it with their calendar. It's also good for fans who want to keep in touch!
(*) The exception to this rule is where the non-player is defined as an alternate contact for a player, usually when they're a parent or guardian to a child on a youth team. See this article for more information on that.