For now, here’s where you can make the real money, if you’re lucky. Publishing houses actually tend to be extremely picky, because they’re looking for marketable material, so make sure you’re starting off on the right foot.
There are two ways of submitting your work to a publishing house: with an agent, which increases your chances of success, but the agent’s going to be taking a cut of the royalties for him or herself, or submit straight to the publisher, which gets you all the royalties, but reduces your options, as there are publishing houses that won’t even look at an unsolicited submission. If you want to find a good agent to represent your book, this is a good place to start. Just press ctrl-f and type in the genre you’re work best fits in to.
Either way the process is largely the same. First, write a submission letter and synopsis. The submission letter should tell the publisher what the story is about, what works it is similar to (without overpraising it, that way lies disaster), and who would be interested in reading it. The synopsis should basically sum up the story in 100 words or less. Think of it as writing the description on the inside of the dust jacket.
If you succeed here, the publisher will ask for an excerpt of the book, do NOT send them the full manuscript yet, just send them some excerpts of what you think is the strongest part of the book. If you impress here, they’ll ask for the whole manuscript, and if you succeed here, then, congratulations, you’re published.
Note that getting published by a big publishing house doesn’t guarantee you’re going to have a bestseller, or that your book will sell at all. It just means that it’ll be mass distributed and maybe ound by prospective readers.