Subdivisions are a must to learn, they are in essence a key to playing time, they are the amount of notes played or counted per beat.
It can get a bit mathematical but bear with me, the most common pulse to count is a quarter note and in most modern music there is 4 quarter notes per measure......counted 1, 2, 3, 4! But the quarter note can be subdivided in to smaller notes, another common subdivision would be eight notes, this would mean there are 8 eights notes per measure.....counted
1 & 2 & 3 & 4 &! we count the &s in between each quarter note giving us 8 notes. this can be subdivided again until we are cramming lots of notes into the same quarter note pulse we original started with. To be honest this whole topic deserves a full lesson in itself so pop on in and were will get you playing and thinking in a few new subdivisions!
Bellow is some sheet music of a subdivision pyramid, put on a metronome to a fairly slow speed (I recommend about 50-70) and start with the quarter notes, from there work your way down the sheet, squeezing the next subdivision into the same pulse. the notes must be spread out equally per beat! good luck