Stick figures outside the box are actors (who). Ovals inside are use cases (their goals). Lines join who can do what. Click an actor, an oval, or a dashed arrow — or press Tour to step through every part.
▸Read it actor-first: follow a stick figure's lines into the box, and every oval you reach is a goal it can pursue. «include» = always reused; «extend» = optional add-on.