Originally Answered: How do you publish a book?
Step 1 - Finish your writing
Step 2 - Find publishers, look up the Writer's Marketplace at your library to find them
Step 3 - Submit a query letter, include a sample, ask if they would like to see more
Step 4 - Submit 100 letters
Step 5 - Get rejected alot, then keep sending those letters
Step 6 - Receive a positive response then get published :)
Agents are only there to help negotiate deals, like contracts with publishers, tour dates, movie rights. They don't help authors get published for the first time, you're on your own. If any agent claims to do so at a fee, it's a scam.
The slush pile is a pile of submitted manuscripts publishers will keep if they need to publish something and they don't have anything better. It's a reserve, something to use just in case. You want to avoid the slush pile so make sure your letter stands out.
Also, don't fall for all those self-publishing scams. You have to pay for everything, do all the work, and major bookstores don't carry self-published books.
Just keep at it and you will be published. Good luck :)