Basically, if taken after a workout, when you are protein and carb loading it breaks down the nutrients and basically shoves the stuff into your cells, esp. nitrogen. This is probably one of the most trickiest hormones of the body, so if you plan on doing insulin, be careful, it's not like roids, once the pancreas stops producing insulin, it will not begin production again once your off, thus making you insulin dependant. I played with it for a little while, and made monster gains, my little brother is diabetic so i was able to attain it easier than roids. It will initially make you leaner as you store more carbs that would otherwise be stored as fat, but it eventually has a tendency to make you fat and the cells develop resistance to insulin in which case circulating excess carbs will be processed as adipose tissue.
Like i said it is usually most effective after training when the body already has a tendency to store more carbs and protein. Start at 2-4 iu's and work your way up a bit, do not go over 1 iu per 20lbs of bodyweight. Again carb load during this phase to to keep from going into a hypoglycemic state. You should take 10 grams of sugar or glucose for every iu taken. If you begin to feel dizzy, sleepy, or weak you should take additional doses of sugar.Mix 150 grams of glucose in water and consume within 20 minutes of injection. Hope i helped, and didn't confuse you too much.