I had a knee injury on monday and today my lower leg and foot are extremely bruised and swollen. what to do?

See a physician: Significant knee injuries can cause calf and foot swelling and bruising. I would see a medical provider to make sure you have not developed a blood clot in your calf. Make sure to elevate leg, ice knee and do ankle pumps frequently to reduce swelling. Assuming there isn't a blood clot, X-rays to rule out a fracture will be needed. An exam can be done and probably MRI to look for ligament damage.