What exactly does an accent mark do to the pronunciation of a syllable?

So this feels like a stupid question but I was wondering how an accent mark actually changes the sound of a word.

For example if I take the word brindar, I can easily recognise and say brindara (for subjunctive past) and brindará for future.

I have no problem recognising these words when they're spoken and using them myself when speaking.

What I haven't thought about however is how the accent mark actually changes the sound.

Is the sound with the accent mark said louder, deeper, faster, slower, with a rising tone, with a falling tone or something else?