My knee pain keeps coming back.

I went to the hospital recently because my knee was hurting, and they told me it was due to a lack of exercise. It stings and worries me. I started some light exercise, but the pain persists, and I'm starting to get scared. I want to manage my knee pain well, so I would appreciate it if you could share some easy exercises or stretches I can do at home. I'm curious how others have overcome this.