What does the "checkpoint passed" mean?
The checkpoint passed sign is actually a button. Before that point you can click on it and test out of all the material prior to the checkpoint button. There should be three checkpoints on your skill tree that can be clicked to test out of the material before it.
Checkpoint passed is when you have passed the checkpoint. It's also a button, and when you press it, it shows up levels you have not learned yet. If you're an expert in Italian, French, etc., you can try it out. Oh yeah, if you make a new account, and try the placement test, you get 350 XP. :) hope this helps!!!