Once your hosting is set up, you need to install a content management system (CMS) for your site. We recommend WordPress because it is easy to use and a beginner (like you!) can quite quickly figure out how it works. Most good hosting providers will have a one-click install option for WordPress, which means it will only take you a couple of minutes and you will have WordPress installed on your site.
The topic you choose must have enough depth that you can create a lot of content for it. This is important for building an authoritative site, for search engine optimization, and most importantly, for the end user. If you don't have enough content about a topic, you're not going to be taken very seriously as an authority on the topic and it's unlikely you can convince someone to make a purchase from you.