A quarter note is a note that represents the duration of one beat. In other words, it gets one beat.
It looks like this:
You remember that I told you that a song in standard (4/4) time gets 4 beats per measure, right? That would mean that the song would get 4 quarter notes per measure because a quarter note gets one beat. That’s why it’s called a quarter note. There are 4 quarters as a whole. For example, a dollar bill can be divided up into 4 quarters.
To strum quarter notes we’ll strum on each beat. In measure one we’ll play the C chord four times on each of the four beats. In measure two we’ll use the same strumming pattern while playing a G chord. In the third measure we’ll change to a D chord and then close things out in measure four with the C chord again.