Interval rides are a very efficient way to improve cardiovascular capability in a relatively short period of time. There are countless types of interval routine you can do, but at its simplest, it involves raising your heart rate significantly for 1 - 4 minutes (can be much longer, but this is a typical length), then having a rest period for 1 - 4 minutes. Then repeat, and repeat, etc. for however long you are scheduled for. These can be hill repeats, sprint work, headwind work, etc.

Endurance rides are done in an endurance zone - the zone you can ride all day in, basically. (If you are using a HRM and actually know your zones, it would be up to mid zone 3) You should have a slightly elevated HR for the times you are climbing, etc., but generally this should be a comfortable talking pace. You can base these on time or miles, but the key is to gradually build up distance/time if that's your goal.

Recovery rides are easy spin out your legs workouts, muffin rides, etc. Generally done the day after a long or hard workout.