Heeya Becca,
I've been playing guitar for nine years now. I taught myself, and now I give lessons. There's all kinds of ways to learn on your own. The big thing that I found out in my own experience is to learn chords, before you learn anything else. A lot of people like to start out with those Mel Bay books, where you learn one note at a time. While that's cool if you want to play classical guitar, or read music properly, it's not very practical for those of us that just want to jam! Get yourself a chord book or just look online, and learn your chords. Start by learning your major, minor, and seventh chords first. As you learn these three types, you'll start to see the similarities between them. You'll also be able to play all kinds of songs.
Youtube is also a great tool. There are sooo many different guitar lessons on there, not to mention that there are detailed videos that show how to play almost any song you would want to learn.
The most important thing though is that you just stick with it. Chords are frustrating! At first they don't sound right, your fingers hurt, and you just feel like your not going to remember the finger positions or be able to switch to these certain fingerings fast enough. Just keep practicing. Everyone goes through that! The more you play the better you will get! Anyone can play guitar, seriously, I'm a living example. It's just the ones that don't give up that get good at it!
Feel free to send me a message if you have any questions about chords or anything else. I'm always happy to help anyone with guitar questions!