There are a number of different ways to go about traditional publishing, but most typically it involves working with a literary agent to sell your manuscript to a publishing house. The agent will work on your behalf to try and get the best deal possible, and will take a percentage of your earnings (usually 15%).
Once you have found an agent, they will typically help you to polish up your manuscript and get it ready for submission to publishers. You'll submit your book to a number of different publishing houses, and if any are interested, they will make you an offer. The publisher will then pay you an advance against future royalties, and will handle the printing, distribution, and marketing of your book.
For more information on traditional publishing, you can check out this link:
https://www.thebalancecareers.com/how-to-get-traditional-publishing-rights-for-your-book-2799589