In 4/4 time we have four beats in a measure and a measure is represented by quarter notes. A dotted quarter note lasts for a beat and a half. So a dotted half note equals three beats. A dotted eighth equals an eighth plus a sixteenth, and so on.
If you watch the video and listen to me play, you'll be able to understand what I am talking about. Dotted notes come up fairly frequently in sheet music, so being able to understand how they work rhythmically with the other notes and durations is important to furthering your musical knowledge.
I also highly recommend you learn lots of different dynamic markings .