Have you ever tried dropping two pieces of paper from the same height, and seen how they fall? You would have seen that the folded piece of paper falls to the ground faster, and more directly than the unfolded paper.
This is due to air resistance.
Air resistance is the force which the air exerts on anything moving through it, which tries to oppose the movement of the body. Anything that falls freely from a height experiences air resistance. However, the amount of force that the air exerts depends on how the body is falling.
This force is determined by the surface area of the body that is falling. The surface area of the body is a measure of how much of the body the force is acting on. If the surface area is more, the air resistance is more, and the body falls more slowly.
For example, when you drop two pieces of paper of the same size- one folded, one unfolded- , the folded piece of paper experiences less air resistance because it has lesser surface area exposed to the air. The unfolded piece has a much greater surface area and hence experiences greater air resistance. Thus the folded paper falls faster than the unfolded paper.
Similarly, we see in skydiving videos that when the skydiver falls straight down, with his body vertical to the direction that he is falling in, he falls fastest, as he faces the least air resistance.
When the skydiver wants to slow down, he makes himself flat against the wind, almost “lying down” in the wind. This increases the surface area and makes him fall slower. When a group of skydivers are seen holding hands and making a formation, they maximise their surface area and slow themselves down a lot.
Finally at the right time, the skydiver opens his parachute to quickly slow himself down to make a safe landing.