Let's break it down:
* Le samedi: Saturday
* après-midi: afternoon
* il: he, she, or it
This phrase sets the scene for an action that occurs on Saturday afternoon, followed by the subject (he, she, or it) who will be performing that action.
For example:
* Le samedi après-midi il va au cinéma: On Saturday afternoon, he goes to the cinema.
* Le samedi après-midi il fait du vélo: On Saturday afternoon, she goes cycling.
* Le samedi après-midi il pleut: On Saturday afternoon, it rains.
Let me know if you'd like to see more examples or have other French phrases you'd like explained!