Greetings and welcome.
With a soft synth, you are recording the midi data, not audio. That midi data is recorded into a midi track and triggers the synth to play the patch or sample in the synth you have selected.
It is recorded like audio in all other ways.....arm the track and press go...start playing on the midi keyboard.
You should see the midi notes being recorded to the track.
Now.... if you are talking about converting that track to audio...... you would select the track and choose bounce to track and click OK.... it will bounce the midi and synth output to a new track as an audio wave.
You can also freeze the synth in the track. I use this for temporary things only. You can unfreeze the synth and edit the midi. The problem with freezing is that the synth is still in the synth rack and MC only allows 8 synths. bounce it and remove the synth and you can use that synth space for a new track & synth. Handy for orchestral things.
Hope this helps..... if not, just ask a more specific question.