HTML is probably my least familiar language out of the few I work with, but it's the first one I learned. Back at the Hazleton Area Academy of Sciences, I took an HTML course that laid the foundation for my interest in programming. Our final project was to build a webpage, but it was such an ugly mess; I can still rememeber the bright blue background and lack of formatting. I'm much more pleased with the glow-up from a designer's perspective.
First, let's talk about a site that'll be a coder's best friend despite the language they'd choose to learn; with 13 languages available, they offer free courses and resources available to anyone willing to learn.
Next, we're hitting a much more web-focused resource offered by the creators of Mozilla Firefox themselves. Focusing on Open Web technologies, it's an indepensible and up-to-date resource for any aspiring developer or designer.
Another "catch-all" website that's geared more towards beginners trying their hand at coding for the first time. As the name implies, their format is much more instructional including Youtube videos on their channel offering minuature lessons.