Quarter notes are 4 beats to a bar.
If we have four even strums in a bar, that is a quarter note
Play the G Major chord counting four beats each bar for one bar.
Now strum the E minor chord for four beats and again for 4 beats. Ending with a whole note on bar 9.
This is a quarter note.
This is all downstrokes.
A quarter note is one beat long.
There are 4 quarter notes to a bar.
Play along with it