The way you make 3 tracks into one is to just do a mixdown. Highlight all 3 in the multitrack, go to EDIT, and select either "Mixdown All Waves" or "Mixdown All Waves To Empty Track X" (and choose either mono or stereo, depending on whether you've panned anything).
I like using the second method, b/c it automatically lines the new track up for you.
As far as how to keep things in time, I'm not sure what you're asking. If you're triple tracking vocals, you need to practice it so you can closely reproduce each track vocally when you record it. It'll never be perfect, but that's what gives multi-layered vocals a thicker sound...otherwise, you'd might as well just make copies of one vocal track...which would be silly. But you want to practice to the point that you can get most of the consonants to line up pretty well so the differences aren't distracting.
Also, if you've got a track that's pretty close, with just a couple of screw ups, then you can right click on one and select "split" and then slide part of one over to the left or right to line it up better.
good luck
