Hello!
Try to rest and do not exert your injured knee and take OTC NSAIDs such as ibuprofen to immediately give you relief from pain.
Apply ice packs and if your pain continues beyond couple of days then you would need scans and a proper examination and diagnosis near an orthopedician.
It is important to rule out bone and ligament injuries if your pain continues beyond 2-3 days.
Take care!
first have it xrayed and go from there. in any trauma-like situation you can't go too wrong with RICE...means Rest, Ice to the area, Compression with an ace bandage for a few days and Elevate the part you injured higher than your heart. In this case, like reclining in a lounger. you would have to decide on any over the counter medications to take or not.