A small dot after any note makes it last half as long again (one and a half times its normal length).
A quarter note 3 which lasts for one beat in * time, lasts for one and a half beats when a dot is placed after it (4). Dotted quarter notes are best counted with "and" between each beat. You will often find them mixed with eighth notes (5).
In the following exercises dotted quarter notes are used in a rock beat.