Externally- I have used it on warts on my skin and it is very effective. Using a cotton ball soaked in vinegar and applied to the wart or taped to the wart for a period of time is how it is done. It is one of those home remedies that can be used on smaller warts to save you the time and expense of a trip to the dermatologist who will likely apply liquid nitrogen. Both treatments are slightly painful, the vinegar moreso depending on the location of the wart.
Observe this:
https://www.youtube.com/watch?v=RxxVhuM9Eu0I was much more aggressive in the amount of vinegar I used than the woman in this video.