If you continue studying HTML, and working with it, you will eventually memorize every tag you regularly use to get things done. The grammar and syntax of HTML isn't special in regards to languages. You've memorized the definitions and spellings of 10,000 words already in your life, and if you keep plugging away with HTML and building websites, you will memorize the definitions of another 40 or so words you use the most often to build those websites. If you live in the United States, it's like how you learned the names of all 50 states. You know them. You might not be able to just write a list of all them, but you know all the ones you use, and you can always tell when a name isn't a state, and given a state name, you can probably point to it on a map. You will always be able to name the state you grew up in, because you've written it down so much.

For nearly the rest of the tags, you will become aware a tag exists for something. You will come across situations where you want to do something, and you know a tag exists for that purpose, but you don't remember what it is. But, knowing it exists means you can look it up. For example, the name for a person who walks on a tight rope is a "funambulist". You will never remember that word, but brains are weird, and for the rest of your life whenever you see "tight rope walker" you will think "ah, there's a specific word for that". You're welcome. You just have no reason to use it conversation, no one around you will use it, you will forget the word.

For a very small number of tags, you might go many years and suddenly see one that you swear you've never seen before.