Tornare means "to return" in the sense of coming back from somewhere. It is interchangeable with ritornare:
Torno dall'Italia. (I'm returning from Italy.)
Le ragazze ritornano stasera. (The girls are coming back tonight.)
Restituire means "to return" in the sense of giving something back:
Mi ha restituito il denaro che mi doveva. (He returned the money he owed me.)
And riportare means "to return" in the sense of bringing or taking something back:
Mi hanno riportato i libri. (They returned my books.)
Hai riportato i libri in biblioteca? (Did you return the books to the library?)