Find a publisher. Look for publishers with a portfolio in your genre of literature or nonfiction. If you write children's books, for example, note the name of the publishing company of the books with which you most identify. A publisher with a strong portfolio in sports or science will be more open to titles in those fields. You should also look into subcategories of literature. Child rearing is a much broader focus than raising children with autism, for instance.
Create a package to send to the publishing companies. Your package should include a cover letter, resume, author's biography and a proposal describing your book. For a nonfiction book, provide a chapter-by-chapter outline. You should also include at least one chapter from your book. For a beginning author, it is advisable to send the entire manuscript.
Contact the publishing companies to find the name of the acquisitions editor, and address your correspondence and proposal to that editor. Some publishers (particularly in nonfiction) allow for electronic submission of proposals. They require you to fill in an online form on the company's website, and to attach any supporting documentation (like your proposal).
Follow up with the acquisitions editor by sending an e-mail or calling. Allow six weeks to pass before following up so that the editor has time to read your work.
Self-publish your book if you are having difficulty finding a publisher, through a subsidy publisher like Lulu or CreateSpace. You will need to learn the technicalities of formatting your book for publishing, including designing your own book cover, though you can hire a graphic designer to help you with this step. Depending on the self-publishing company you choose, you can print a large number of books, or have the books printed one by one to order (this is called "print on demand"). You can then sell your books through websites like Amazon or Barnes and Noble.