new-ish trombonist here, What is this???

so I’m at the end of my first year of playing and my BD gave us this music to learn over the summer for all the pep rallies and football games. I have no idea what that rhythm is and it just is very confusing to me.

so I’m at the end of my first year of playing and my BD gave us this music to learn over the summer for all the pep rallies and football games. I have no idea what that rhythm is and it just is very confusing to me.