Understand the difference between true online self-publishing and vanity press publishing. This is a fine line. A vanity press publisher will charge you to publish your book. A print on demand publisher charges you set-up fees to prepare your book for print. In either case you pay money, but a vanity press publisher will typically take your money, print your books, and ship them to you with no marketing plans. Most vanity press operations promise to publish your book without even seeing the manuscript. This is a red flag. Any legitimate publisher will want to see your manuscript before they know whether they can publish it. This doesn't mean you should not pay to have your book published if you are self-publishing, but the money you spend should go toward legitimate printing and marketing costs.
Use an online publishing option such as LuLu or Amazon (see Resources). These services allow you to upload your novel and format it online. They also offer options for selling your novel online. These companies print and ship your books to customers as they are ordered, saving you the cost of having to print and store hundreds of copies of your books at a time. Using one of these services is as simple as uploading your manuscript and choosing your design features. Once you've done that, your book is in the system and ready to sell.
Use an online service specializing in adult material if you have a novel for adults-only (see Resources). eXcessica is an online publisher of adult material that publishes your novel in e-book or print format. It doesn't charge anything for the service. Submit your manuscript for review and if it's accepted, eXcessica will publish it for you and pay royalties to you by PayPal or by mail. eXcessica will even provide cover art for your novel at no charge.