After the attack on Mr. Weasley, he gathered up all the Weasleys and Harry in his office and made one out of a tea kettle. He had it lead to Number 12, Grimmauld Place where they could stay with Sirius over Christmas break because it was closer to St. Mungo’s then the burrow, and thereby a better place for them to be able to see their dad.
After Sirius’s death and Dumbledore’s duel with Voldemort, Harry is sent back to Hogwarts via a portkey made on-the-spot by Dumbledore.
