Take your theme that you have installed on your hosting account or make a new site and add a theme (it’s your choice).
Create a child theme and customise it using CSS and HTML (you can even try PHP if you are feeling brave). Add relevant elements to enhance your SEO. (permalinks, tags, categories etc).
The main idea here is to play around with the various options available for customisation.
Show us before and afters and your process, with a link to your site.