Thanks for writing in! You can setup a local server, install WordPress and test your X theme on your PC or Mac as well. To do that refer to the following resources.
Or else you need a hosting account to host your domain. You don't need to go with WordPress hosting, but you can select any affordable hosting plan that you would like. However make sure that your hosting provider has PHP v5.6.x or higher.
Once you setup and install X theme, you can start building websites using Cornerstone builder. You can access our knowledge base section from there following link (https://theme.co/apex/forum/t/knowledge-base-overview/287) which you can find helpful articles.
Hope that helps.