Following the below steps you can easily bulk create Teams in your TeamGenius account to add players to after tryouts. 

First click on Teams in the top menu and then click on Manage Teams.

Next click on Import Teams on the right side of the screen.

Click on Select CSV to Upload. 

You can download a sample CSV file to see how your upload of teams needs to be formatted. 

Next click on Confirm and Import.  (Note that Teams and Coaches are both options to import with this tool)