In order to create a team, account administrators (Account Owner or Administrators) can click on "Settings" > "Teams" > "Create a new Team".
You'll then have to choose a Team Manager (i.e. a member which is able to see all his/her team's payments) and choose the name of your team.
You can then add members in one or several teams (the same member can belong to different teams).
☝️ If you've created teams before having invited members, don't worry you're able to allocate a new members in one or several teams directly from the "Invitations" tab, if you need to.