Look for deformity, retractions with inspirations, or a displaced trachea. Observe rate, depth and effort of breathing. Listen for wheezes, etc. Check for areas of pain, masses, and feel for the movement of the chest on deep inspiration. Fremitus is decreased with pnuemothorax and increased when transmission of sound is increased as though consolidated lung of lobar pneumonia.
Percussion is used to determine if the underlying tissues are air or fluid filled or solid.
Using the middle finger's distal joint press firmly on the chest keeping the rest of the hand off. Then strike the DIP joint with your other middle finger tip-movement is from the wrist. Normal lung tissue is resonant. The liver sound is dull. The lungs sound dull when fluid replaces air in the lungs as in pneumonia with infiltrate or with hemothorax.