Traditional publishing looks like this:
Write. Seriously, before you even start thinking about how you're going to be published, you have to write. You must have a finished, polished book before you can begin to head down the path to publication.
Revise. No. I'm serious. You have to write your book, you have to polish your book and you need to know it's the best it can be before you read the rest of this. Don't put the cart before the horse. You know what happens when you do that? YOU RUIN YOUR CART AND HURT YOUR HORSE. (In this metaphor, your cart = dreams, horse = book. DON'T DO IT.)
Query. You'll need to learn to write a query letter. You'll need to have that letter critiqued. You'll need to compile a list of agents. You'll need to query those agents. You'll need to learn about how to Revise and Resubmit, and you'll need to understand how to Nudge.
Get an agent. When you get an offer, have a list of questions ready to ask that agent. Have a lawyer look over your contract. Understand your rights, and what you owe to the agent/agency.
Go on submission. This is mostly your agent's job, and you'll be basically sitting and waiting for updates and sweating your brains out (metaphorically, I hope).
Get a deal. Again: Ask questions, have a lawyer look it over, understand your rights and what you owe the publisher.
Get an editor.
Marketing. Even with a traditional publishing house behind you, you will be expected to do a fair amount of marketing. You'll need to know how to use social media. You'll need to do blog tours and possibly signings. You might have to travel to attend conferences and make appearances at which you will likely be largely ignored.
BOOK GETS PUBLISHED.
If you are looking for more information about the more personal side of each of these steps, Dahlia Adler has some excellent resources. She is an editor, and slushpile reader, and an author. She has spent endless hours interviewing people in every step of the process to get their reactions and their experiences. Her Perpetual WIPs series interviews (anonymous) people who are querying, people who have finished querying and are agented, authors who are on the pre-published path, the elusive agents who make it all happen, and authors who have been published.
Also, check the sidebar. There are links to lots of writers who have shared their stories of being published and getting agented and everything else having to do with this crazy business. Follow them on twitter, read what they say, familiarize yourself with the process. It may be changing, but the overall system has remained pretty much the same for a long time, and any major changes will be big news.