Hello, I'm 13 and I have a large amount of pain in my knee, preferably in the Articular cartalige (sorry I suck balls at spelling). I don't play any sports but I'm on vacation right now and I have done a lot of walking and running, I haven't tried anything yet so I'm open for suggestions. When I walk down a small flight of stairs and I contract and extend the muscles in my knee, I feel pain, and crap load of it. So please help me, this really hurts. And to answer your possible question, NO I didn't smack my knee against anything.

Have you told your parents? Their insurance would cover you for a doctor's or chiropractor exam. And I strongly urge you to deal with it now when it's fresh and you're young. Ignored knee pain and injuries don't get better when left alone. Your knees are critically important for holding you upright, for walking, running, etc.

Running on uneven surfaces can damage a knee, because one leg is landing on a higher spot than the other. Classic places are along roads, which appear level and smooth but which dip down on the edges for water runoff, and beaches.
Your knees have sacs of synovial fluid, which can leak out, causing friction of joints that hurts a lot. There are tendons and meniscus, and so on! It's almost impossible to diagnose your own knees.

Yes, stay off that knee! Soak in tubs, move it gently every few minutes, sleep with a pillow between your knees when you are on your side.

Often the first step is simply the old RICE recommendation and see if you get any relief. Rest it, ice it, use some compression, and elevate it. If you don't have any known problems with it, something like ibuprofen might help with any inflammation and pain. If it continues, or you've had issues with it before, get it checked out. Some knee injuries can go from bad to worse, and more extensive treatment becomes necessary.