You can add people to a workspace only on the Team plan, and only workspace owners can do it.
To add members to a workspace:
Click the workspace name in the top left corner.
At the bottom of the list, select Settings and Members.
From there, you can invite new users.
The team plan includes 3 members by default; Each additional member is charged 15$ per user.
📌 If you don’t see the Settings and Members option, you’re not the workspace owner.