Ur patella underneath osteo changes making way for fluids to leak from its barriers

Laser physiotherapy and quadriceps exercise

Chiropractic adjustment will help. Contrast Fomentation (Hot and Cold). Avoid Squatting-

You didn't mention your history, but it does look like there some trauma to your knee, either sports related or accident or fall. As mentioned, there's a sprain of one ligament, possible tear of medial meniscus and strain of muscle on front of your thigh. Though these problems are mild, they need to be addressed through physio therapy otherwise, problems may worsen with constant swelling.

First of all for swelling use cold water Fomentation. Along with that u need to start Physiotherapy earliest possible because all these issues can improved after Physiotherapy. Avoid excess knee bending in any activity.

It seems that you had an injury, consult a physiotherapist for proper treatment.