I fell 3 days ago down stairs and fell and rolled ontop of the top of my left foot, there is a big noticable lump and hurts to the touch & wen I walk?

See a doctor . It is important to have the foot checked and an x-ray performed to make sure it is okay.
You need to . See a podiatrist or orthopod to have a clinical exam which likely will include an x-ray to make sure you did not sustain a fracture. The lump may be a contusion, fracture or injured tendon. Ice it and take antiinflammatories until you can get to a doctor.