How do I create a subpage using HTML

It should be the same as making a JS subpage, only you're coding it in HTML

The HTML and CSS course teach how to code in the language. You are suppose to gather all the knowledge you know and create a subpage (or whatever website you want). However, your website may not look very good, but as you continue to learn about the language you will be able to create all kinds of fancy, creative, and amazing websites. So like Electric Dolphin said, "It should be the same as making a JS subpage, only you're coding it in HTML."