Manos al aire literally translates to "hands in the air", the universal sign of surrender. It's a phrase you might hear in an action movie when someone gives up a fight.
In this powerful song, Nelly Furtado uses it as a metaphor for surrendering in a relationship. She sings, "yo no tengo armas para enfrentarte, pongo mis manos al aire" (I don't have weapons to face you, I put my hands in the air), vividly expressing her decision to choose love and vulnerability over continuing a painful conflict.
Have you ever been in an argument where the other person just completely loses it? That's exactly what Nelly Furtado is singing about here. Her partner is losing control, talking loudly, and telling her to shut up. She sings, "Tú / Que pierdes el control / Hablando en alta voz / Hieres mi corazón" (You / who loses control / speaking in a loud voice / you hurt my heart). It's a really frustrating situation, and she feels like she can't get a word in.
But instead of fighting back, she does something completely different. She gives up the fight. The title of the song literally means "Hands in the Air," and that's her big move. She declares, "Y yo no tengo armas / Para enfrentarte / Pongo mis manos / Manos al aire" (And I don't have weapons / to face you / I put my hands / hands in the air). For her, winning the argument isn't the point. She just wants to get back to the love they used to have, singing that all she cares about is loving him "Como era ayer" (like it was yesterday).