Create a dataview of the team and place a listview or datagrid containing the players. Then create the logic to add or remove players to the team. And you might want to do some learining paths like this one where the basics of Mendix is explained: https://academy.mendix.com/link/paths/40/Mendix-Basics or this one if you have some developer experience: https://academy.mendix.com/link/paths/82/Crash-Course
Regards,
Ronald