I just dabbed it with my finger around the base of the nail and along the edges where it meets the skin. That is where the fungus starts. I put enough on so it was very wet. Not sure about vinegar for athlete's foot, never had it. With the nail fungus, you have to make sure that you do it twice a day until a completely new nail has formed, and then for a couple months thereafter, otherwise, the fungus can jump to the new nail from the old and you will have to start the process all over again.