The Team Member feature works as to give a free account the benefits of a paid account. As to say, if you have a paid account you can give your team members access to all the paid features, but not access to your account nor can they give you access to theirs.
To add your Team Members go to My Account >> Team members >> Paste the email of the account you want to add then click on "Add member".
By adding an account as your Team Member you won't be giving them access to your social accounts. Only, if both of you add the same profiles or pages you will be able to see and edit each other's scheduled posts, and the same doesn't go for events and groups.