Postural drainage involves using gravity and different body positions to clear secretions from the lungs. The document describes various positions to drain different areas of the lungs, such as sitting forward or back in a chair for the upper lobes, or lying on the side or stomach in a Trendelenburg position for the middle and lower lobes. It also mentions percussion and vibration are used along with positioning during the procedure, and aftercare is the same as for chest physiotherapy.