every little step
you'll want to make sure that you uncheck the 'R' for record on the old tracks so you don't accidentally record on that track (although depending how you have it set it won't delete the old track, but you can set it to do that). Then make a new audio track, go to it on the event view (where you see the waveforms etc), select which input you want to use for it, hit 'R' to arm it for recording, and then hit the record button up top. You might also want to hit the little wave button on the track to monitor it while you record, but depending on your soundcard you might get a lot of latency and not wanna do that. Hmmm, I guess you also need to make sure that the old tracks are using an output that is active or you won't hear them. each track has a selector for input and output. I don't think i'm leaving anything out. hope this helps, sonar is complicated to use at first, but it's WELL worth it once you get used to it (it's really the best for multitracking, and all around).