Right now, I wouldn't worry too much about exact intensity percentages. Figure out a simple HIIT routine, try it, and make adjustments as needed. For example, for a 20-minute stationary bike routine, warm up for 3 minutes, then up the intensity a little to a good solid pace for the fourth minute. Then, after four minutes, up the resistance by 5 and do a steady sprint for 45 seconds. It doesn't have to be completely balls out, just good intensity. Then go back to the regular pace for one minute, then sprint for 45, etc.. Start with something like that and change the resistance and interval times as you like.
I do this 2-3 times a week on the bike, cross trainer, stair climber, treadmill, whatever. Once you get with a comfortable routine, it will be easier for you to figure out what your percentages are.