R.I.C.E.S Rest, Ice, Compression, Elevation, Support. Ice as much as you can, 20 minutes at a time, stay off of it as much as you can, elevate it above your heart as much as you can, support it with a compression wrap. Get an MRI, they will tell you what's wrong within two days. If you need surgery, you will get surgery, if you need Physical Therapy, they will sign you up for PT appointments. There they will give you exercises to strengthen your leg.
Strengthening your quad and hamstring has proven to help prevent major knee injuries. So after this situation has passed, start lifting legs, run more, do everything you can to get your legs stronger. You will be sore, and it will suck dick but it must happen if you want to be able to any physical activity which involves your legs.