Does the epidural completely numb you from the waist down? How can you walk?

You don't. There are walking epidurals which use very low doses of local anesthesia and opioids to give pain relief. You will not be nimb, but you will be comfortable. You should never try and walk without help if you have an epidural. If the "walking epidural doesn't help enough, then you may need stronger medicine and in that case you won't.