Welcome to the web! There are so many ways to learn web dev, and this is just a quick sampling of what you might want to do.
First, if you’ve never actually done any HTML or CSS coding before, you might want to start with a popular interactive tool with immediate feedback, such as one of these:
Khan Academy Intro HTML and CSS
W3Schools Tutorials for HTML and CSS
Or better yet, all of them! One of the most important things to learn as a web developer is to find multiple experts and resources. Even experts don’t always agree about the best way to do something as a web developer, and doubly so for how to teach and learn web development.
Once you’ve got the basics, you have a whole world of options! If you already know about a project you want to work on, that’s a fantastic way to continue. You might want to look into more online tutorials, books, workshops and courses. Many self-taught web developers dive straight into reading the code of existing websites using browser tools, and then trying to duplicate the features. A nice in-between step is using a hosted community where people can publish small projects and snippets, such as one of these:
Repl.it Tutorials and Community Projects
Here at AAA Web Dev, multiple resources for learning Web Dev are available in the “Web Dev” dropdown of the main menu, including a page full of Repl.it starter projects. These resources also include a legacy version of a Web Dev curriculum used in classrooms, currently in the process of transitioning to a fully-online format.
Have fun, and happy coding!