This is probably the most popular stroke. It is the one use the most for improving or maintaining fitness, and it is the one that is learn first by most swimmers. For most swimmers free style is their fastest stroke.
Although freestyle is done on the front, if done correctly, the swimmer should only be on their front for a very brief period during each stroke. The swimmer should be tilting from side to side. E.g. when the right arm is pulling the swimmer should be on their right side. As the left arm enters the water the swimmer should be tilting towards the left. This helps the swimmer get a better pull, puts less stress on the shoulder, helps the opposite arm recover, and reduces resistance through the water.
During the recover phase the recovering arm starts from the hip. The elbow is lifted high while the hand just kind of hangs down from the elbow. This is the quickest (and less stressful for the shoulder) way for recovery to occur. At no point should the hand be higher than the shoulder. The hand should be in the air until it reaches the spot just in front of the forehead. At this point the fingers enter the water first then the arm is straightened out.
During the propulsion phase the hand should pull in a slight "S" shape. This is done so the hand is constantly pulling on 'new' water that is not moving. This is the best way to create propulsion. The hand should be under the body, but should not cross over to the other side. The hand should also accelerate as it pulls under the body (so the speed increases). Then the propulsion phase is completed as the hand reaches the hip. Ideally, the arm should be fully stretched out to the side before entering the recovery phase. If the hand is pulled out of the water too soon then the swimmer loses part of the propulsion they could otherwise get.
Breathing can be done either on one side only every stroke. Or it can be bilateral. Bilateral means that the swimmer alternates breathing on both sides, but every 3rd stroke. In training, the coach may reduce the breathing rate, e.g. every 5 or every 7 strokes. This helps the athlete train with less oxygen in the body. Early swimmers may find this very difficult. The swimmer should never hold their breath. While underwater the swimmer should be exhaling.
Flutter kicking is used for propulsion but also for balance. Ideally the swimmer should try and get about 4-8 kicks per stroke. Small fast kicks are best. Ideally the feet should be slightly under the water. If the feet are splashing this is an indication of wasted energy.