Poke the hanging hook into the top of the bag (that's the side without the hose, if you got a closed-top bag), and assembley is complete!
The first step is to head to the local drug store and buy an enema kit.
The longer an enema is in you, the better it works, with 15 minutes being almost universally cited as the best time to retain an enema.
You don't have to hold it the full 15 minutes, of course, but it is suggested.
The "official" enema procedure is to start on your left side, roll to your right side halfway through, then roll again a couple more times, but this really doesn't increase the effectiveness much, so just lie down however is comfortable to you...
on your right side, left side, on your back, or however else you want to.
Get out the lube, and put a good glob on your finger.