While good and true advise, it would also be helpful to provide some type of references/suggestions to get a new person's research started. Here are a couple of suggestions:
Here is an online
saltwater beginner's guide with several good links included.
Also, there are many good books out there. You can probably find several at your local library. A good one that I like, and have seen many others recommend as well is
The conscientious marine aquarist by Robert Fenner. It has lots of great information, from equipment to concepts, to guides on many fish species. A great "all purpose" guide.
Here is a link to some
beginner fish possibilities. Just be sure that you are paying special attention to understanding a fish's requirements before you buy, so that you don't end up setting yourself up for failure. In particular, pay attention to tank size recommendations and nutritional needs.
That should get you started. As you read, lots of questions will undoubtedly come up so just remember...Google is your friend. Feel free to post anything you need help with or clarification on.