Sounds like you don't need a manual as much as you need a good classic book on recording. Yes you need a mixer to work with a device like this. You'll also need a separate 2-track device of some sort to mix down to -- either another r2r machine, a cassette deck, DAT, computer, CD recorder, or whatever.
Check the local library and see if you can find a copy of "The billboard guide to home recording", preferably an older edition. Or any book on recording published before about 2000 should have some good info for you.
ask some of the guys in the analog forum for some good info for newbies; they'd probably have better links for you than I would.