lulu.com has a self publishing service and they can send out your book to amazon and a few other booksellers. It's about $60 to do. The only thing is, there are no editors there for you, so you have to do all of that work yourself. If you want to get published by an actual company, go to your library, find books of the same genre and find their publishers. Send them a query. Only if they are interested in your query should you send them a manuscript. Act as if they are the only publisher in the world (only submit to maybe 3 publishers at a time but dont let them know!) There is a lot of info and samples of queries and manuscript formats on about.com
your manuscript is just your book, set in the proper format (look here: [link]) those are the guidelines as well. If you have any guidelines for them, you do not mention it. it can make them not want to publish it if you throw that at them in advance. If they want it, they will contact you and you can give them your guidelines then. I'm pretty sure it's the same thing all over the world.
Have you finished the story you want to publish? If so, you should probably go over it and edit it to the point of perfection, then edit some more, then maybe find someone else to help you edit, and after several thousands of hours of editing you can start a cover letter and research publishers that are keen on whatever kinds of material you have. There is a book that is published every year in the reference section at most Barnes and Nobles called Writer's Market full of publishers, which is a start.
If you haven't finished your story, then it's not a book and you don't need to be worrying about publishing at all.
I'd recommend looking into writer's conventions in your area. I've heard they can be essential for a beginner in terms of marketing, so get your google fired up and do your homework.
You can self publish a book. There are companies that will let you pay them and they'll publish your book for you. This is an easy way to get your book out there, but if your book comes from a self-publishing company, it won't get as much prestige as a book published by a "real" publishing company. For someone just starting out, it's not a bad option.
Getting yourself published with a traditional agency is tough. Just think about how many people must be sending these agencies their work. Your best options with that would be figuring out a way to get yourself noticed publicly, or getting work in the writing or publishing field so you have a chance to meet the right people. I can't say for certain which firms are the best.
There are about a billion different ways to advertise anything these days. Just think about how you see other books being advertised. That's how yours would be.
Agents aren't there for getting your work published as much as they are there to get you money in negotiations. If you have work that a publisher thinks is good enough to get them money, they'll publish it, even if you're being represented by a five year old. No agent just means the publishing agency will take more of the profits.
Essentially the steps are 1. Finish the book 2. Send it to the publisher
But it's not all that simple. There's no laid out plan for the secret steps between one and two. I'd make sure your work is perfected, and decide weather you want to self-publish or not. If you don't, just start getting involved in the writing community online and in person so you have a chance to meet the right people. You can try sending your stuff to publishers right away, but don't depend on that working.