When you invite someone to a Bubble, they can contribute media to that bubble, and they have the ability to manage and edit any media that they have added to that bubble. They will NOT be able to edit or manage media that is contributed by others to that bubble. They will NOT have access to any aspect of your account other than the particular bubble you have invited them to.
As an Account Admin, to invite someone to your Business Account, go to your Dashboard, select the Users tab on the lefthand side, and choose to "Add New User" with the green + icon. You will be prompted to enter their email, name, and select the role you would like them to occupy (Account Admin, Content Manager or Contributor).
Account Admin- has control over everything in the Business Account (including adding new users).
Content Manager- can do/see pretty much everything in the Business Account, aside from managing users.
Contributor- can only contribute & manage their own media, and only have visibility to information and statistics related to their own media.