Originally I planed to buy an ordinary 6 string acoustic guitar, but now I saw that 12 string on ebay. It?s just about $ 120, so I really consider buying that one, as I heard that the sound of a 12 string is much better. But the problem is that I don?t really know how to play it. How do you use these extra stings??

Hope you can tell me something about it!
well you can do some crazy 12 string stuff like nile does, or for chords, just take 2 strings per same note, like if you playing a power chord, do it with 4 strings, not 2
12 sting can sound better - most noticably fuller sound, but as John Butler and company and they will tell you that it's hell on your fingers and nails - especially if you enjoy fingerpicking. Can also be tough on your left hand (assuming you're a right-handed player), especially bare-chords higher up the neck. But essentially, you pay it like a regular 6-string. Cheers
essentially if you grabbed a six string guitar that was an octave up then normal and then paired the strings up with the normal strings and you would have a 12 string guitar

6 string tuning

12 String tuning
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