In Book 10, Odysseus decides to leave Circe's island. She decides to help him with the rest of his journey. She helps him in a few ways.
First of all, she tells him that he is going to need to go to the land of the dead to get advice from the ghost of Teiresias. The ghost will tell him how to get home.
After Odysseus gets back from the land of the dead, he goes back to Circe and she gives him more good advice. She is the one who tells him how he should get past the Sirens and the Scylla and Charybdis. She also tells him not to kill the sun god's cattle.