After you've added all of the teams to your division you can now invite everyone to join FlipGive via your club/league page.
Families and supporters can self-select the team they belong on and as long as they use the invite link you provide for them they will be able to sign up and automatically join their selected team.
To get the invite link, login to your club/league admin console and click on the "Send Invites" link on the left navigation. Then click on the "Email" option and "Open in email client" - there you can customize this email as it contains the link as well as the invite code required for team managers to join the teams you setup. Share this with your distribution list and everyone will be 3 clicks away from joining their team!