Go to Divisions from your User Home page. Be sure the correct season and competition are selected. Click on by the appropriate division. Click on Add Teams to Division.
By default only the teams with the same play characteristics (age group, gender, level of play) will be displayed in the selection list. If you want teams from outside the division's play characteristics, you can check "Show All Teams in League" to see them.
NOTE: A division can have a range of age groups, in which case all the teams matching ANY age group in its range will be displayed by default.
You can select multiple teams by holding down the Ctrl key (or Apple key on a Mac) as you click. Teams previously added to the division will not be displayed.
When you have selected the teams, click on . A list of the teams in that division will be displayed. You can edit or remove a team from the division by clicking on the appropriate button next to the team on the Divisions page.