Find a suitable domain name. You need a website on which to set up your ebook store. Select a domain name that is relevant to the title or titles that you intend to sell. Ideally the title of the book itself would be a great domain name, but it is likely that the book's publisher owns this. Use Google's keyword tool to see what search terms people are using. Type in a relevant keyword and the tool will return the most frequently searched-for term of relevance.
Purchase your domain name. Use a domain registrar or, if suitable, a website-hosting company that also handles domain registrations. Once you own the domain name, begin setting up your website.
Populate your website. There are many one-click installs that enable you to make a website even with no web design knowledge. Wordpress and Tumblr are two popular options. Select the relevant option from the dashboard of your hosting account to install.
Install your preferred ecommerce software. There are two ways of doing this. You can use an ecommerce plugin such as eProduct or you can register as an affiliate with an ebook retailer like clickbank. Using an ecommerce plugin is most suitable if you are selling your own book. Clickbank is suitable for selling other people's work. Clickbank affiliates have access to links and banners which they host on their site. If a customer clicks the link and purchases the book, the affiliate receives a commission.
Promote your site. You can do this many ways. Set up a Google adwords account to buy advertisements for specific searches. Optimize your website by tailoring the content to have a high keyword density. Supply content for other sites in return for a link to your site. Links pointing to your site increase your site's page rank, which means it has a higher placing in Google search results.