The goal here is to be able to accent every possible 16th note in a very simple strum pattern. Of course the accent will happen in places you would not usually put it, so at the beginning, this might feel a bit odd. You will realize right away that this exercise will give you more control over your right hand strumming.
I advice to mentally count the 16th notes in this way:
1-e-&-ah, 2-e-&-ah, 3-e-&-ah, 4-e-&-ah
where 1,2,3,4 are your beats in 4/4 bar.
So the first exercise will put an accent on your ‘1,2,3,4’
The second exercise will put an accent on the e’s of every beat
The third exercise will put an accent on the &’s of every beat
The fourth exercise will put an accent on the ah’s of every beat
In better words, you are playing an accent on the 1st, the 2nd, the 3rd and the 4th 16th note of every beat.