Hi!
Open the recording VU meter from the View menu. Click on the 'Record to' button and select the track to which you want to record. If you want to record all the takes to the 1st track, you should select 'Record to track 1' from the recording VU meter every time. Now when you hit 'record' the new part will be recorded in track 1. A word of caution here, don't forget to position the cursor at the desired place on the time line before recording or you will end up recording over a previously recorded take in the track. Though this is not such a big problem and can be rectified, it should definitely be avoided.
Alternatively, if you want to do multiple takes in a song using many tracks, one trick which i use is as follows. Open a new file in n-Track and insert a drum track in the first track at the same tempo as that of the original song(you can also use n-track's built-in metronome though) record the new take on the 2nd track listening to the drum track in track 1. Now select the part of the take(or the whole file, as the case may be), copy it and paste it in the desired track (and desired place) in the osiginal song. This way you an eliminate 'lag' while recording.
btw, what are you trying to record? Send me an e-mail giving more details regarding what you are trying to accomplish so that i can help you better.
Good Luck!
Soundking.