I have been bit by a spider and don't know what kind and now after three day i have a hole in my foot. what should i do?

See a doctor: This sounds like a brown recluse or "fiddle back" spider bite. They are very common throughout much of the us this causes necrosis (the hole in your foot). Although not life-threatening, it is extremely serious and needs to be treated asap.

See doc: You could start with e.G some neosporin to wound and take anti inflammatory med like ibuprofen, but need to see your doc to determine if antibiotics or debridement are necessary. Occasionally some medications can be prescribed that minimize extension.