Team guests must be specifically added to projects and don't have access to any projects in that team by default. It's the perfect role for anyone you're working with who doesn't require full access to the team or who will only be working with your team for a short time, like clients, contractors and interns.

You can easily add guests by clicking on the "Shared with" button next to the filter button.

This opens a dropdown with "Invite guests" button. Click this to open a form where you'll enter the name (if the user has already been added to your organization) or email address (if not a member of your organization) of the person you want to add.

Now, when you click on the Members link at the bottom of the task sidebar and click on the Guest tab, you'll see the guest listed there. You can invite them to new projects or change their permissions by clicking the edit icon that appears when you hover over their name.

Both General organization members and Limited members can be added as guests depending on whether the team is locked or unlocked. If a team is locked, a small lock icon will appear before to its name on the Teams page.

General organization members have access to all unlocked teams by default so if you attempt to add them as a guest they will be added as a member instead. Limited members can be added as guests in unlocked teams. If the team is locked and you invite either a General or Limited member, they will be successfully added as a guest because neither role has access to the team by default. Organization Owners cannot be added as guests because they have access to all of the Organization's locked and unlocked teams. You can learn how to lock or unlock a team and make other changes to your team here.