As a novice, I have to say it's really complicated to recognize the official and appropriate HTML specification.
After going through the freecodecamp certification, I had a strong need to read complete specification of HTML, so I could have accurate information about this topic and was not misled by information from unofficial sites like w3schools (even though it's quite elaborate stuff). Wikipedia led me to the WHATWG site, which has large HTML documentation called Living Standard. On the other hand, there is W3C recommendation, where you can read a specification, too.
I would like to ask only one thing: What standard is used by browsers? What is the stuff I should learn from, so I will not have problems when coding later?
Today, http://w3.org/TR/html5/ redirects to https://html.spec.whatwg.org/multipage/
Browser support is variable. https://caniuse.com is a useful reference.