There are things that can't be explained
It happens the same to English in some contexts
Yes, it is necessary. Because in Portoguese the possessive adjectives need the articles. Which is different in English. If I say "It's your book" in English, in Portoguese I mean "É o teu livro", just like in Italian I say "È il tuo libro". That's why learning Portoguese in English is much harder for Latin-language speakers.
But I thought that in spoken Brazilian Portuguese the article before the possessive adjective is not used. Please correct me on this point.
That is correct for Brazilian Portuguese - the article is not always necessary. European Portuguese differs in this matter - you could say it is a lot more formal (such as not using a gente for most cases of the first person plural, unlike in Brazil), but it is just one of the niche parts of the language which separates Brazil from Portugal.
Why was "Eu leio tuas palavras" wrong and "Eu leio as tuas palavras" right?
Muito obrigada também por ajuda-me antes. Eu não sei if that sentence made sense haha but the best way for me to learn is to try to speak and write it even if I'm very wrong hahaha
Obrigado por também ter me ajudado antes** =) Sim, nunca deixe de praticar. Essa é a melhor forma de aprender.
Both forms are grammatically correct, but if you use "tuas" with someone older than you or someone you don't know, you would result quite rude. Same if you say "suas" when you are handing over a coffee to a friend of yours in a bar: your friend would look at you quite puzzled ;)
Why is that? Sorry if this seems like dumb question. Just need elaboration.
Interesting. At first I thought it sounded strange to use "as" but I'm a Spanish speaker and when I thought of how you would say this in Spanish it made more sense to me. It would say "Yo leo las palabras tuyas" but in my usual common talk I would say "Yo leo tus palabras", even though I'm not sure if that's correct to say, I would say it that way but it definitely sounds more accurate using "las" so I'm guessing it is the same for Portuguese. It must sound correct to use "as".
I think in English when I use Duolingo because that's what I set it to English/Portuguese and I can't help but to use Spanish to make sense of all of this and bridge the languages somehow.