I'm a 14 year old girl who owns a guitar.
But I have no idea how to play it. I want to teach myself, because I do not want to spend any money for a tutor or anything.
I do have some music experience. I also play the cello and I know how to play the viola.
Any advice? I'd really like to learn.
First off, congrats! I tried the viola and couldn't play it even with a tutor. Playing a guitar is pretty similar but what I would recommend is first learning to read guitar tab. Essentially what it is is a diagram of the fretboard and the fret number your supposed to hit on that string.
Secondly, get an ear for tuning or a tuner. If you know how to tune your cello or viola then tuning a guitar to the same note isn't hard at all.
Thirdly, pick up some exorcises. Find some strumming warm-ups and stuff to train your fingers. Soloing with a guitar pick compared to a bow is totally different. =)
Lastly, be patient. Your first year of learning will seem endlessly slow and may seem to lack results but if you stick to warm-ups and practicing then you will have it down in no time.