I bought a real book to help me play jazz in my schools jazz band and i play guitar the book says its for "C" ?

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You got the right one. Guitar is a "C" instrument, meaning that the notes written on the paper are the same notes you will hear. Instruments like the trumpet and saxophone are what you call "transposing" instruments. Which means that the note written on the paper isn't the note you'll hear. There's a few reasons for this, but the important thing to know is that if you're going to play with transposing instruments, their music is going to be written in a different key. That's why they have the different Real Books.

No, you can play in any key on the guitar!. The pieces in your book might all be in the key of C but it's not difficult to transpose them to other keys.