After registering and linking your account, the team captain needs to create a team. All you need to do is to go HERE and click the "create team" button.
Once it's done, a new team will appear on THIS PAGE.
Next to it you will see a gear icon - click on it and then press the "manage team" button. On this page, among other things, you can find a link you can send your teammates, so they can join you.