So this is my NEW favorite workout! As you can see, it uses only your own body weight, no equipment (except for a chair or bench), and is fairly "easy" to do. And when I say "easy," what I really should say is simple. These are not needlessly complex moves where you have to contort your body into impossible positions. The moves are straightforward and easy to comprehend.
Basically, you perform the exercises for the number of seconds or reps stated under each exercise, until you've done that entire circuit (grouping of 3 exercises). Then you rest for about 60 seconds. Then do the next circuit. Then rest for 60 seconds. Then perform the next circuit. See the pattern here? You can perform the entire amount of exercises twice or three times through if you want, or only once all the way through if that's all you can do.
Heck, so what if you can't do all of the exercises or as many reps as it says. At least you're moving, right? With continued practice, you'll get stronger and soon you'll be able to perform all of these a couple of times through.
For the chair step-ups, I use my plain wood kitchen chair and put it up against the wall so it can't slide backward while I'm stepping on it.
I personally add an additional touch of cardio to this routine: In between each circuit of three exercises, I do about a minute of jumping jacks or mountain climbers. Then I rest for about a minute before continuing with the rest of the exercises.
The idea with these exercises is to perform them as quickly as good form allows, so that you're body works at near capacity, then you only rest for a short amount of time in between moves, so your heart rate stays elevated (but not through the roof!) for the duration of the session. The thinking is that you can burn around the same amount of calories doing a harder workout for say, 20 minutes, as you would doing an easier workout for 40 minutes.