Sailing theory involves understanding how a sailboat moves through water using wind power. The key concepts include the interaction between the wind and the sails, which create lift similar to an airplane wing. By adjusting the angle of the sails, sailors can harness the wind's energy to propel the boat forward, even against the wind by using techniques like tacking. Another important aspect of sailing theory is the concept of buoyancy, which allows the boat to float. This is governed by Archimedes' principle, stating that a floating object displaces a volume of water equal to its weight. Understanding these principles helps sailors navigate effectively and safely.