One very simple hook you can make is called a Gorge Hook. The hook is usually fashioned out of bone or wood. It is sharp on both ends and the string is tied around the middle. The middle of the hook has a notch in it so that the string wont slip away.
One of the downsides of the Gorge Hook is that the fish usually will swallow it and the fish will have to be killed to retrieve your hook. Still good knowledge to know.