The knee is a very complex structure. This accounts for the reason why the knee can be injured easily, and why treatment of certain knee issues can be difficult. Not all knee injuries occur in isolation. That means that someone with an anterior cruciate ligament tear may also have a meniscus tear or another cartilage injury.
This video on knee anatomy is quite thorough and will provide you with a nice overview of the knee and serve as a good starting point as you seek to learn more about your knee and what the source of your knee pain may be.
When you have finished watching this knee anatomy video you should have a firm grasp on the bones, muscles, tendons, ligaments, joints and bursae around the knee. Then we can get into particulars about how each can be afflicted to cause you discomfort.
For more information on specific injuries to the knee, please see the sections on: