So there are different ways to do a steam. You could go sit in a sauna. That would steam your entire body. They also make these cool things that you can set your face on and it and it will generate steam from the water you put in. But there's an even simpler way...
Boil some water, and give it a couple minutes to cool slightly. Then pour the water into a bowl, put your head over the bowl, and then put a towel over your head, so that it traps the steam under the towel. That's as simple as it is! I don't know why anyone would spend money on something when they already have everything they need!
So why would you do this? Its a great way to deep clean your skin. The steam will open up your pores and then the steam will be able get deep into your pores to further clean your skin. If you have some breakouts that just wont come to the surface, this is a really great way to clear your skin up. The steam will also moisturize your skin.
I would recommend steaming your face after cleansing, but before moisturizing or using a facial mask. You want to make sure your skin is clean though, that way the dirt and make up can't go even further into your skin, and by moisturizing after, you will get the most out of your moisturizer. If you don't plan on moisturizing or anything, then I would say to go ahead and splash your face with some cold water to close your pores back up.
You can do this once a week for about 10 minutes. But you can adjust this as your skin needs it. If your skin is congested, you can obviously do this more than once a week. Also, make sure you're not putting your face too close to the water so you don't burn your skin. Obviously, you will know if you're burning yourself.
Have fun, and good luck steaming!