There are many different reasons for knee pain. Consult your healthcare provider.
If you have knee arthritis – go to Arthritis
80% of your knee strength is from your quads. Exercise is your friend.If you have arthritis, exercise can help pain. If exercise is not possible, ask your doctor if a knee injection will help. Usually cortisone is used.
The safest exercise for knees is running in deep water. If you don’t have a pool readily available, then using a stationary bicycle is great for knees. Make sure your leg is almost straight when your pedal is at the lowest point.
A common cause of knee pain is patello-femoral syndrome– You don’t have to bend your knees as much as the person who is demonstrating the exercise. Just bend the knees to a point of comfort.
Here is a knee pain program that you can try from PainBC.ca
Pain at the back of the knee with swelling, could be a popliteal bursa – Baker’s Cyst.