How did the sword of Gryffindor kill the basilisk?
In 1993, Harry Potter stabbed the roof of the basilisks mouth with Godric Gryffindors Sword and ended up getting a fang splintered into his arm. In 1998, during the Battle of Hogwarts, Ron and Hermione went down to the Chamber of Secrets and destroyed Helga Hufflepuffs Cup with a basilisk fang.
Why didnt the basilisk fang kill Harry?
The basilisks poison was strong enough to destroy a horcrux, making fans wonder why the one in Harry didnt die when he was bitten by the giant serpent. As it turns out, Fawkes not only saved Harry but also the part of Voldemorts soul living in him.