I just got a Q10 last week and used that feature. The Q10 has 4 "insert" jacks on the back that correspond to inputs 1-4 on the front. This is a "standard" insert mechanism, and hopefully you understand the concept.
Anyway, you need an "insert" type Y-adapter cable. This is basically one that has 1/4 stereo male jack on one end, and 2 "mono" 1/4 jacks on the other. You plug the 1/4 stereo jack into the desired "insert jack" on the back of the Q10. Then you plug one of the mono jacks into the INPUT on your other device (reverb unit, compressor/limiter, etc), and then the other mono jack into the OUTPUT. SPECIAL NOTE: One of the MONO jacks is considered the "TIP" and the other is the "RING". You need to check the Q10 manual to be sure which goes into the INPUT and OUTPUT of the other device. The Q10 manual has a section that describes this (I don't recall if TIP goes into the INPUT or vice versa, but the Q10 manual tells you.)
In case you don't understand the concept, it's really simple, the signal from Q10 comes the Q10 preamp, and then out to the INSERT jack. The Y cable sends the signal out to one of the mono plugs which goes into the INPUT of the external device. The other mono plug, carries the OUTPUT back into the Q10's insert jack. At that point, the signal goes on through the Q10 and into your PC and into your recording software. The recording software has no knowledge of the external device.
This works great for using a compressor/limiter on the mic's before it gets into the PC and recorded. This can also work well for reverb, but depending on exactly what you're trying to do, you might have things differently.
Hope this helps.