To create a team, go to the Teams tab of the Home page (see: Home and Explore Page). Click on the ‘New Team’ button, and choose a name for your team. Click the ‘Create’ button to create your team.
Users are currently limited to creating one team each. If you need more teams than that, the support team will be able to help you - click on your avatar in the top-right-hand corner of the screen and select ‘Contact Support’.