You are able to invite others if you are either an owner or an admin in the team. If you are not, contact your team admin, otherwise ask us and we can help you out.
To invite others, go to the cog icon on the top right of the screen.
Then add email addresses of the people you'd like to invite.
If you are wondering about the roles, read about them on this page.
Everyone invited will get an email to the team.