To do that you need to go to your Account Settings, open Team section and type in an email address of the person you want to add to your team.
After the invitation is sent please ask your team mate to confirm it from his/her email.
As soon as the invitation is confirmed your new team member is able to access all your reports and share your report and subscription limits. Team management and lists are inaccessible for team members. However, they can create their own lists choosing either they want to share with the team or keep them private.
Additionally, owner of the main account can remove added seats when needed.