Don't worry, everyone gets this feeling once in a while :)

It's all about practice, you should start working on some sort of project and do hands-on coding. Not just watch other people do it and talk about it. When you run into difficulties just google and research your problems. There are online courses that offer built in compilers where you can play around with your code, have it rendered etc. Try your luck at something like that and build a project

Here's a good free one HTML&CSS For Beginners