Make it available at your website, and offer it as a freebie to other websites who attract the people who would be interested in your e-book. There are lots of other options if you hope to make some money on sales. You still do the marketing, just as in any other publishing venture, but they handle the technical aspects of creating the book, order fulfillment, etc. Similarly, you can contract with one of the subsidy e-publishers who charge to format and make your book available. They accept anyone who can pay, so acceptance is not an issue.
Costs vary widely.
Again, you do the marketing. How available the e-book is depends on the publisher. You can create an e-book yourself using Adobe PDF or other formats. Then, market and sell the book from your website and others. They format it as a secure PDF file, then offer it for sale.