I got myself set up on WordPress.com, before this course advised NOT to use it. Oh well. But, I'm assuming that the website design interface looks much the same as the one you are using via wordpress.net. If so, look at the left hand navigation panel, and find "appearance". There's a sub-folder called "themes" and it will show you all the different themes that are available. You can pick them, and try them out. Or you can start with a blank sheet, and build your own. I have used "Twenty Twenty-One" which seems to be an all round, generic website, and I'm pretty pleased with what I've got (but not enough to have actually published and gone live!).