There are two ways to ban a user from your team. You can either perform the action from the team directory in the team workspace or from the Dashboard. When a user is banned from the team is immediately kicked out and cannot join again.
Expand the Team Directory and locate the user you want to ban and click to expand the menu. Select the "Ban from Team" and the user will be kicked out of your team.
Please note that only the team members who have the ban permission can ban other users. You can set the permission in the Dashboard → Roles & Permissions
Alternatively, you can ban a user from the Dashboard → Users