when he returned to hogwarts hagrid told harry hermione and ron about what?

If I'm not mistaken, Hagrid told them where he was gone. This might be in a later book, but I'm pretty sure that Hagrid, being half-giant, had been sent by Dumbledore to make peace with the giants, who the dark side were trying to win over. Hagrid met his brother Grawp there, and he told the trio that he had brought Grawp back with himself and he was in the Forbidden Forest. He might have shown Grawp to them.