The word Spaniards say more than any other

Vale

BAH-leh — Okay / alright / got it

"¿Vamos al cine esta noche? — ¡Vale!"
Shall we go to the movies tonight? — Sure!

Textbooks love "de acuerdo," but in real conversation in Spain, "vale" is what you'll actually hear — for agreeing, confirming, or just acknowledging what someone said, like a verbal nod.

"Honestly, I probably say this fifty times a day without even noticing — my students love catching me doing it mid-lesson."— Graciela