How do you write well?
Depends. You mostly have to follow or cleverly subvert accepted syntax and grammar rules. Keep your information nice and organized. Writing doesn't usually have a question as much as a prompt.
What even is the English language?
It's so complicated y'all. It's this mashup of German syntax with Latin-derived words and dozens of other borrowed words from other languages. It has so many irregular verb forms and conjugations that aren't intuitive. We even have additional verbs we add to our verbs to denote tense and voice and permission. But at least we don't have gender and noun declension.
How does online slang affect how we communicate?
Online slang is a form of code-switching where you know to use certain syntax and language in one realm versus the other (unless you're fearless and bring these to all areas of your life). Semantically there are unique spellings of English words (like "smol") that connote something entirely different from its "proper" spelling. In some circles, communities build their own connotations and context for already-established words that an outsider might have a hard time picking up on right away. And no, it doesn't necessarily make us less intelligent in our use of English, Baby Boomers.