Collagen makes up a lot of the material found in bones, teeth, ligaments and tendons. As we age, collagen levels become depleted and this leads to a more fragile body (and wrinkles). Some people have a higher collagen content than others.
Collagen has many uses outside of the body. One of those uses is in gelatin. Gelatin is found in many of the foods we eat, including jello. It is also used in some glues. The oldest glue dates back 8000 years and collagen was used to make it.
It also has medical uses as well. It is used in burn victims as a skin substitute and it is used in certain cosmetic surgery procedures.