In order to add users to a project, the users need to be added at the account level by an admin first. Here's how an admin can add new users at the account level:
Navigate to the Account level by clicking the BUILDR logo in the top left corner.
Navigate to the Team tab.
Click New User on the right hand side and enter their information.
Removing a user from Buildr is just as easy. Deactivating a user removes them from all projects (user can no longer sign into Buildr). If you wish to add or remove a user from just one project, that can be done in the project's Team section.
To Deactivate a User (completely remove them from Buildr):
Navigate to Team at the account level.
Click the trash icon next to the user you wish to remove.
Click Deactivate User at the bottom of the pop up window.