External users have similar rights to regular users but can’t share tasks, folders, or projects, and they aren't included in the My Team group. External users can only see the contact information of people who share common tasks, folders, and projects with them.
External users are able to:
Access and create tasks, folders, projects, and spaces through the List View, Table View, Gantt Chart, and Activity Stream.
Access the My to-do and the Inbox tab.
See, comment on, and attach files to tasks, folders, and projects shared with them
Change the status of a task.
Export reports shared with them (reports are only available on Business and Enterprise accounts).
A detailed chart comparing the rights of license types, and what each can and can't do, is available on our User Rights by License Type help page.