I had a dark brown spot under my foot and was very small and look like a callus but now i have like four more and was wondering what it can be?

Many things: The dark brown could indicate bleeding which happens when a wound is beneath a callus or within a wart. Any pigmented lesion should be examined by a doctor

Wart: Warts and callous do closely resemble each other, especially on the thick skin on the bottom of the foot. The darkened area can be a blood vessel within the wart. Remove all doubt and see a specialist.