Watch the Blues for Two online guitar lesson by Mimi Fox from Jazz Performance

Dynamics are a subtle but very important aspect of music to learn. You could start by arbitrarily and somewhat randomly trying to play softer/louder. You might try to shape a line or a phrase by starting at one level and then coming up/down in volume as the phrase ends. Notice how this impacts the phrase. Notice the impact on you, the listener! Listen to recordings of Billie Holiday and you will hear a master at using dynamics to color and shade the phrases she is singing.