You will need to route the output of the instrument/aux track to a bus, which you then in turn route to the input of an audio track (preferably stereo).
Then record enable that audio track, and hit record.
If you want to add a reverb there are two ways I would recommend doing it.
1. Make a send from your audio track to a bus, then route that bus to the input of an aux track. Then on that aux track place a reverb (D-Verb for example) in one of the insert slots. Switch the "mix" amount on the reverb to 100% then use the fader on that aux to control the reverb level.
2. Insert the reverb plugin in one of the insert slots on the audio track and use the "mix" amount to adjust the reverb ratio.