Assuming you don't intend to self publish, there are two routes you can take.
First you have to identify books like yours and see who published them. Visit at least three bookstores not in the same chain. Figure out where each would shelve your book if it were already published. Photograph that area, subtly, then go home and ID the publisher of every title. That's your A-list.
Look up each publisher online. If they have a link for authors, submission guidelines, like that, follow what it says and contact them with exactly what they ask for. Most of the publishers who deal directly with the author are small presses. (E-publishers do this, too.)
If you see nothing like that at the publisher's website, that means they deal only with literary agents. You return to your pictures and find out the names of the agents who brokered each deal. Find their websites (and other social media) and follow their instructions for submission. Typically they want a query letter and either sample pages or a synopsis.
Neither publishers nor agents want to see writing that's anything less than fully polished. A final draft, completely free of errors, no typos, no missing words, no grammatical mistakes (except in dialogue), properly punctuated, is what they expect--and what your competition is sending.