"Acho que falando se aprende mais rápido." = "I think that speaking is a more faster way to learn."

In this case, the pronoun "se" is used to universalizing the statement. It's like saying "you learn faster by speaking". You put "you" in that sentence, but you're talking about a general fact.

Just replace 'se' by 'one', and I think you will understand. Acho que uma pessoa aprende mais rápido quando fala. => Acho que, quando fala, uma pessoa aprende mais rápido. => Acho que, falando, uma pessoa aprende mais rápido. => Acho que falando se aprende mais rápido. "Se" may have the function of the indeterminate subject, though it is syntactically used as if it were an object. É-se muito feliz em Portugal => Uma pessoa é muito feliz em Portugal.

In English, we can say: I think that speaking we learn faster. In this frase "acho" means opinion ( I think or I believe, I Guess). And you believe that the fast way to learn is speaking. So, achar means Find (to find something) or achar means to have an opinion ( I think about; I guess, I believe). I'm learning English and I hope I have helped you.

I think that speaking is a more faster way to learn. Em inglês, essa frase fica assim. Espero ter andado