How to tell if sprained my knee?

I was leaving my rehearsals when i jumped in the air and when i did my knee popped. Instant pain in my left knee right where the doctor checks your reflexes and the meniscus area. i'm not sure if i sprained my knee or not but i can walk on it and it hurts quite a bit i think i tore my meniscus. when i twist it will hurt to and there is some swelling by my left knee reflex