Just what is a twelve string?
A 12 string is a 6 string, with double the strings! The second set of strings are tuned one octave higher (except for high b and high e), and are played at the same time. Playing a 12 string is a lot like playing a six string guitar in feeling, but it produces a really cool chorus sound. The fretboard and nut are wider than a six string to accommodate, but the pairs of strings are close together so it's not too much harder to play.
12 strings are most commonly used as accompaniment, not as a solo instrument. This doesn't mean you can't, but it is definitely harder to play more than chords on this instrument. 12 string guitars can be heard on hotel California - the eagles, and free fallin’ - tom petty, as well as many other classic hits.