From my point of view Publishing can broken down into three main types: Traditional, Self and Electronic.

Traditional publishing, as you can probably guess, is publishing through a publishing house such as Scholastic, Random House, Houghton-Mifflin, etc. (just to name a few big ones). Publishing your book through this kind of channel is generally considered to have the most potential for the author to become a "best-selling" author due to the established and proven distribution most publishers enjoy. However, this is also viewed as the most difficult to attain. Publishers rarely accept unsolicited manuscripts and on the whole prefer to receive manuscripts from unpublished authors through literary agents instead.

Self publishing is just that. Publishing (printing, binding and distributing) your book on your own. There are many companies that can assist individuals with this type of publishing, the most well known of which is probably iUniverse. Since this is done on the individual level it is very easy to 'get published' because as long as you have the money to afford printing a few copies (getting an ISBN is optional, but highly recommended) then anyone can get published through this medium. If you just want a copy of your manuscript "in print", this is your best option.

Electronic publishing is the newest trend and involves distributing your book in an electronic format such as PDF. There is little cost for this kind of publishing, and as a result anyone can distribute their work in this manner. In fact, anyone can set themselves up as an independent publisher this way. In theory this is the best way to get your manuscript read by a wide audience for little cost, but the fact is that the majority of consumers buy their books through major publishers at bookstores (both online and at physical locations).