How did the the Aztecs do the sacrifice?

They laid the person who is going to be sacrificed on a altar and, with a special, flint knife, they take out the person's heart. This was offered to the gods.

Another form of sacrifice was body skinning. The chief, who was trained to do so, took off the person's skin in one piece. He then wore it for 20 days and walked around the village. It was then burned.