I'll try to help a little (even though you may have already figured it out by now).
Chapter 8 of the ST User Guide explains PAD mode. When you have selected your LOOP under the INSTRUMENT & PLAY tabs, look at the top bar (red). From
right to left you'll see EDIT, MIX, PLAY, and then a keyPAD. Press that and the PAD grid window appears. It's mainly for a drum pad midi controller; but it can be "played" by clicking your mouse on any of the pads.
I'll try and explain how to get the LOOP into your DAW by using PATTERNS (since a LOOP is just a PATTERN that repeats)
Using PATTERNS in your DAW is literally a "drag'n'drop". I'll use ST drum patterns as an example.
• In your DAW, add about 8-10 empty tracks
• Use the top track to select ST3 as the instrument FX
• Move the ST3 window over so you can see it AND your DAW tracks at the same time (important)
• Pick any drum kit in the Instrument tab (got to start with the actual instrument before a PATTERN can be heard). Your track in DAW will probably show that Instrument Label once you've selected it. DON'T CLOSE THE ST3 WINDOW!
• Click the PATTERN tab in ST3, then select your Instrument, then it's genre (Rock, Techno, etc.)
• You should now see a sub menu with things like Chorus1, Chorus2, Fill1, Fill2, Verse1, Verse2, Intro, Outro
• Here's the fun part: Drag'n'Drop each of those over to the empty tracks under the top track, then be sure to change the Track LABEL to reflect what PATTERN it contains. You should see the Midi note patterns in each of the tracks.
No FX is needed for these tracks; they merely hold the pattern to be copied.
See YouTube video below• You can now "build" the entire drum part of your song in the TOP track (with the FX loaded) by simply copying each of the items in the lower tracks and dropping them where you need them.
• When you've completed the build, simply hit play. The TOP track has the FX loaded and is the only one that you will hear with all the assembled parts.
• Word of caution if your DAW is like Reaper - It's tempting to make the TOP track a FOLDER with all the PATTERN tracks below it the CHILD/STEM. But then you'll have a mess in the TOP track because a FOLDER PARENT automatically copies in all the other tracks inside the FOLDER. But of course, you can turn off all those if you like the idea of a FOLDER. I take the precaution of making the "mess" a REGION with it's own color when it do that.
** Under the new v 5.11 of Reaper you can do all this in a SUBMIX.
Okay now back to your LOOPS. (I have not actually tried this, so maybe DanielIK can confirm).
Hopefully from the above explanation you can see that when you select the VSTi from your DAW and ST3 window pops up:
• you put the two windows side-by-side
• you pick your INSTRUMENT LOOP in ST3, and is reflected in your DAW Track FX track
• with both windows open, arm your DAW track to RECORD
• over in the ST3 window hit the loop key of your choice on the virtual keyboard to start it looping
• Back in the DAW window, hit RECORD
• The DAW track should start being populated with the LOOP midi notes until you hit STOP in the DAW.
I sure hope this is actually the way it works for LOOPS. The PATTERN exercise has helped me understand the relationship between the DAW and the VSTi FX.
This YouTube should help you wrap your head around the concept. It mistakenly calls the "Drag'n'Drop" items LOOPs; but they are actually PATTERNS:
VST Drum Tracks in Reaper -
https://youtu.be/xg2dBfYCbx0