Domains are entirely separate from hosting.
While hosting is the service you pay to host your website's files, domains serve more like a mailing address to tell your browser where to look for your website server and files.
Having a domain is not necessary for installing Semplice, and in many cases people choose to build their Semplice site on a temporary domain until they are ready to replace their current website and domain. For example Flywheel (our favorite hosting provider) assigns a temporary domain to your Wordpress install.
If you are curious about how our licenses work with domains, you can read more about licensing here.
Pointing a domain
If you need to 'point' an existing domain you have registered to your Semplice site, we recommend getting in touch with your domain registrar as they will be able to assist with this further.