If Caliban learns anything in this play it is from his interaction with Stephano and Trinculo.  When he first meets them, he ends up thinking that Stephano is a god.  He thinks Stephano will rescue him from Prospero.

What he ends up learning (by Act V, Scene 1) is that the other people in the world are not better than Prospero.  He thinks that Stephano will save him, but Stephano doesn't really care about Caliban either.

So Caliban learns that people other than Prospero are willing to exploit him and enslave him as well.  That is why Caliban ends up calling himself a fool for thinking that Stephano was a god (in Act V, Scene 1).