Only the studio owner can send invitations so others can become studio members.
Every studio has an "owner" who can extend invitations to others on your team so they can become studio "members". If you don't know who the owner of your studio is, or to change studio ownership, contact firstname.lastname@example.org.
If you are the studio owner, simply scroll down to the MEMBERS section on the left-side navigation bar in your studio, and click the "+" sign to initiate an invitation via email. You will receive an email notification when your invitation has been accepted.