Sometimes the only way to tell the difference between two words with the same literal meaning is to observe how they are used in practice. Tornare, restituire, and riportare all mean "to return," but each has a slightly different shade of meaning.

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?)