You have not studied reading and writing formally, but the convertible words already answer most questions about how a letter sounds. When unsure, look back to a word you know.
Spanish has a default stress position, decided by the last letter of the word.
n or s → stress the penultimate syllable
Why those letters? Because they are what verbs end in. Look at the present tense: habla, hablan, hablas, hablamos, all stressed on the second-to-last syllable, with no written accent. And every "to" form ends in r, so the stress goes on the end: comer, estar, hablar, encontrar.
diferente · importante · adictivo · salud (ends in d, so stressed on the end)
Unlike French, the written accent never changes the vowel sound. It only tells you the stress has gone somewhere the rule would not predict.
So every -ión word carries one, and so does every point-past form like encontró, habló, llamó, llegó, vivió. Words that obey the rule need nothing: encuentro, vive.
The other use. Where two one-syllable words are spelled the same, one takes an accent to tell them apart. It does not change the pronunciation.
The ambiguity is real in writing. Sí lo quiero is yes, I want it, but without the accent you could read if I want it.
Where the same word serves as a question word and as something else, the question version carries an accent.
Same for cómo (how) against como (like, as).
This is fine detail, and many Spanish speakers get these wrong in writing themselves. It is here so that an accent you did not expect makes sense when you meet it.
The accent rules are easy to keep because you only need to look at the present tense to reconstruct them.
Verbs end in vowels, n's or s's, and the present tense always stresses the penultimate syllable with no written accent.
The one exception is estar, which does carry written accents: estás, está, están. That is the same exception you met when learning it.