can someone please explain to me what embouchure means?

an embouchure is the way you position you mouth sort of. I learned that very low notes are for the biggest hole with your mouth and the higher you get the tighter your embounchre gets.

It means "face" in french. The french really pionered the modenr brass technique, so we use their word for it. Apeture is the word used to describe the center part of your lips, which actually controls the pitches.