A recovery ride is a short (45-60 min), easy effort. For most riders, this means no hills. With my clients, I don't let them go into the big ring. This is actually one of those rides best done on a stationary trainer, at the gym or on a flat bike path. You want a consistent effort (no stop & go). This type of ride is best done immediately after your hard rides, later that day, or early the next morning. The purpose is to circulate some blood/oxygen to your fatigued muscles and also flush out waste products. This will help you recover faster (thus the name). Sitting on the couch is not considered recovery.

There is a difference between recovery and rest. Recovery is active (ie a recovery ride). Rest is a day off (ie sitting on the couch). Both are necessary in your training.

Regarding cadence, either focus on your normal preferred cadence or just slightly lower. If a lower cadence, you might find you feel more comfortable in a slightly harder gear.