Here's a collection of guidebooks and tutorials that give the basics of HTML, CSS and JavaScript – three languages that form the basis for the modern web. The Mozilla links are documents that you can read through. The CodeCademy and other sites are interactive tutorials to get used to writing code.
For future projects, install Visual Studio Code, which is a handy text editor, useful for more than just web development (you can take interview notes in it, for example).
I think the fastest way to get up and running is to write using the Svelte REPL, which is an online interface for writing HTML, CSS and JavaScript. You can use it as a playground for quick experiments and following along with some of the tutorials.