You can get the basic knee exercises by searching the web for ACL or meniscus rehabilitation exercises.
My opinion is you should not play through joint pain and may want to stop all tennis and exercise until you see an orthopedist. Most say it is OK to play through minor muscle pain but you should not play through joint pain. Rest, Ice, Compression, and Elevation until the pain subsides. Then start rehab exercises slowly - stop if pain or swelling is significant.