Three Levels of Dynamics with Castle on the Hill
This groove uses three levels of dynamics: an accented stroke, a regular stroke and a marcato. You're probably familiar with and comfortable playing accented strokes. They add to a groove by creating a second level of dynamics.
Marcatos are similar, but a marcato is played a little louder than the accented strokes, creating a third level of dynamics. Marcatos are technically "accents," but you can think of them as a stronger accent than usual.