Well the easiest option is self-publishing, but self-publishing doesn't yield the best results in terms of readership. There's some websites and companies out there that offer that, Lulu.com and Channillo.com are some examples off the top of my head. Although Channillo is different in that you'd be publishing your work as an actual installment-based series, and it will cost money for membership.
Traditional publishing would involve sending query letters to publishing companies in hopes they'll pick up your manuscript (or in hiring an agent I guess > >.) Googling "How to write a good query letter for a publisher" should turn up some good results on that. It'd also be a good idea to look up the publisher you have in mind and see if they have guidelines on submissions, like the format they'd want it to be in or the genre they're looking for, especially if it's an online company. I know that typically they're going to want to see the first three chapters of your book, or at least three chapters in general, either before or after the query letter. And don't put it in a fancy font, they hate that
I must stress that your manuscript be as polished and completed as possible at the time that you start submitting it places, especially the sample that the publishers will be reading.
If publishers aren't biting it's a good idea to keep trying to build a name for yourself in the publishing business. I've been advised that even stuff like submitting poems or short stories to magazines, even if it's not the work you want published, will help when it comes to the writing world.