If the tear in the cartilage is not large and if you are not an athlete or are doing some sort of work that puts a lot of stress on your knee, your doctor may very well recommend conservative therapy, perhaps using a brace, and letting the cartilage heal on its own. When your knee can handle it, you may be given exercises to help build up the muscle in your leg to help protect your knee.
However, for larger tears or if you are very active, surgery may be the solution.