You, as a Space Admin, can add users to a team in two ways: adding members to a team from within the team and adding a user to teams from within the user.
Select Home from the menu beneath your avatar.
Click the All Teams link in the sidebar.
Select the desired Team by clicking on the View Team button for it.
Click the Edit Team button.
Scroll down to the Members section and click the plus sign.
Make a list of the individuals you want to add by entering their user ids in the field presented and then selecting them from the resulting list.
Click Add Members.
Select Settings at the bottom of the sidebar.
Select Users from the menus presented in the sidebar.
Select the desired user by clicking on their username.
Check the desired teams and save the user.