Did snakes use to have feet?

Yes - snakes & lizards share a common ancestor. Snakes however, evolved to crawl on their belly rather than walk on their limbs. Over thousands of generations, their limbs got shorter and shorter until they just dosappeared altogether.

You can still see the remnants of hind legs in the 'old world' pythons such as the Royal Python (Python regius) - if you look at the underside of the snake where the vent is, you'll see two tiny 'spurs'. These are all that remains of the snakes legs.

See related link for a picture courtesy of Wikipedia.