The Difference between Collaborators and Team Members
Team Members are users that are added to your Team, they can create new projects, share files and can invite users to projects on your team.
A Collaborator is a user you can invite into an individual project, they will not have access to, or any visibility into other projects on your team.
Adding users to your project as a Collaborator
To add a Collaborator to a project, open the project and click the (+) plus user sign at the top right, if the user is already added to your account you can search for them by name or you can invite them by email address 🙌