There are many types of cartilage in our body, each with a slightly different function. For instance, the medial and lateral meniscus (discussed below) are made up of fibrocartilage which make them strong and rubbery and able to add additional stability to the knee. On the other hand, like bones of most joints, the end of the femur and tibia and the undersurface of the patella are covered in hyaline cartilage. Hyaline (also known as articular) cartilage is both flexible and slippery. The flexibility helps it to act as a shock absorber. Articular cartilage is made even more slippery by an oily lubricant made within the joint, called synovial fluid. This allows the two bones to move smoothly on each other without pain. If this articular cartilage wears away, joint movement can become painful and limited (this is known as arthritis). Unfortunately, cartilage has almost no blood supply and is very bad at repairing itself.
The medial meniscus is a crescent shaped structure that exists on the inside of the knee. It is made of fibrocartilage. It acts as a shock absorber in the knee and adds stability to the knee joint. It is attached to the tibia as well as to the joint capsule of the knee.
The lateral meniscus sits on the lateral tibial plateau. It is a crescent shaped structure that is also made up of fibrocartilage. It acts as a shock absorber in the knee and adds stability to the knee joint. It is attached to the joint capsule of the knee as well. It is somewhat more mobile than the medial meniscus.
In a healthy knee, the rubbery menisci act as shock absorbers. They both sit on top of the tibia and help to spread the load of the femur over a larger surface area on the tibia. If the menisci are removed (because they are torn, etc.) the underlying articular cartilage sees a heavier load and is at risk of wearing down faster (i.e. development of osteoarthritis)