Learning to code is all about understanding a few core principles of a language and then knowing how to use the internet as a reference to accomplish what you're trying to do.
Just like you don't know every word in the dictionary, you won't remember every tag in HTML or every property in CSS. Get comfortable searching for what you want to achieve and learn as you go.
Remember, people made these tools for someone like you to make extraordinary things, and you can do it.
The key pieces you'll need to understand are HTML and CSS. MDN's Getting Started with the web is a good, free resource to get you started until DWC's own tutorials are ready.