This summary is not the rule. The rule text controls.
When someone is appointed to be a tutor (a person who takes care of a minor's affairs), they need to complete a couple of steps before they can officially start acting in that role. First, they must post the required security, which is usually a bond that protects the minor's interests. Second, they must take an oath promising to carry out their duties properly.
Once both of these steps are done, the court clerk gives the tutor an official document called "letters of tutorship." This document carries the court's seal and name, and it acts as proof that the person has been legally appointed and has met all the requirements to serve as tutor.
Think of these letters as the tutor's official proof of authority. Banks, schools, doctors, and other people or organizations can look at this document to confirm that the tutor really has the legal right to make decisions and handle matters for the minor.