I fell know from my knee going down its swollen and painful, when i try walking my knee feels like it gets locked. what can i do for this?

Clot? Infection?: Does "from knee going down" mean swelling and soreness of the lower leg? If so, this could be thrombophlebitis (blood clot in your leg) or cellulitis (skin infection). If the knee itself is swollen and painful, maybe some kind of arthritis. Presumably no injury, right? Any of these could be serious, so don't take chances: see a doctor ASAP. Do it immediatley if pain is severe or if any fever.