Since many publishers no longer accept unsolicited manuscripts, you need an agent.
You need to have a finished novel, in proper manuscript format. You select appropriate agent and send them a query letter, synopsis, and/or sample chpaters as per their guidelines. If they are interested, they will ask to see the whole novel. If they believe it is ready to be published and that they can sell it in the current market, they will contract with your to represent your novel to editors at publishing houses.
Agents act as a filtering mechanism for publishers, a buffer between author and editor in case problems arise, negotiates contracts, tracks royalties, and help manage your writing career. They get paid a commission off what they can sell your work for, and they are worth every dime of that commission.
You need to get more familiar with how publishing really works so you do not end up falling victim to a scam (and there are a lot of scams out there). Some of what you need to know
--the difference between traditional and self publishing and why self publishing has a poor reputation in the industry
--what proper manuscript format is
--why word count and genre are important
--how to write a query letter and synopsis
--the difference between copyright and publishing rights
--what unsolicited means
--what an advance is and how royalties really work
--how selling to the magazine markets is different from the book markets
--what an agent does for an author besides sell manuscripts to editors at publishing houses
--how to spot a scam before it bites you and your bank account
Traditional publishing is free (all development, marketing, and distribution is at the publisher's expense, not yours). Self publishing costs you money - hundreds or thousands of dollars (and all the development, marketing, and distribution is at your expense). Most stores and libraries do not want self published work, for a lot of reasons (and you need to know what those are).
1 - real publishers pay you, you do not pay them
2 - real agents get paid after they sell your work, not before
3 - being "available to order online" is not the same as having books on shelves at real stores
4 - beware of ads and answerers who promote self publishing companies (they are not interested in helping you publish, they are interested in your money)