I have a C edition jazz fake book that I use for guitar. I read about bassists using fake books in their playing. Are they using the same fake books as other C instuments? Is so, how would I use it? It has chords and melody lines but I don't see how I'd get the bass line out of it. ???

The bass line is improvised using the chords.

If the song has a distinctive bass line that is necessary for the song to be recognized, it is often included. If it's a walking bass line (pretty common), it's all improv by the bassist using the chords in the book.

Yeah thats pretty much it. Also you should try to listen to some songs with those type of "feels" to figure out some common rhythms and line styles (like "medium bossa" or "latin" or "swing",etc). Then you can do what you like (or get influence from other recordings) with the lines and improvise with the chords. Knowing what the melody is also helps a bit but not necessary the books are usually just for the tempos and chord changes for bassists.