When creating an in-house league for a tennis club or HOA, normally the "teams" are already known/established and just need to be setup in TennisPoint.
Here are the steps for alerting the team captains that their team is ready to go:
Click on the team's playing level (mens singles 3.0 in this instance).
Click on the "players" tab (also could be called "pairings" for doubles leagues and also "teams" for traditional team leagues).
Top right corner of the page click on the Send Signup Email to Players button. This will allow you as the league administrator to craft a specific email to your league's captains inviting them to the new league you just created.