You can create and manage teams from the dashboard.
As soon as you've created a team, you will be shown the team overview.
There's no limit on how many members a team can have. You can invite others by entering their username or email address and selecting 'Add Member.' They will get a notification (the bell icon in the header) in CodeSandbox and email when invited to a new team. From there, they can accept or decline the invitation.
You can choose which team you're in from the team drop-down at the top-left on the dashboard. You can create new sandboxes directly from here or from a different team, select one or more sandboxes, right-click and select 'Move to Folder', where you can choose the team and folder you want to move them into. All sandboxes in a team can be seen or edited by other team members, depending on their permission levels. We keep track of who created the sandbox, though, and only the original creator of the sandbox can delete it.
You and other members can open a sandbox at the same time and see each other's cursor to work together. You can still invite other people who aren't members of the team to the sandbox or live session.