Drill bits are cylindrical in shape and come in an array of various sizes (reflecting the diameter of the shank). They are inserted into the front barrel of the drill, known as the chuck. The chuck turns clockwise which closes three small metal jaws together, as well as slightly pushing them forward. Turning the chuck counter-clockwise moves the three jaws farther apart and slightly backward. Cordless drills have chucks that are turned by hand, though drills with cords have chuck keys to loosen or tighten them around the drill bit.
Place one hand on the drill's chuck and turn it counter-clockwise. When the chuck's jaws are wide enough, push the blunt end of the drill bit into the center end of the chuck between the three jaws.
Hold the drill bit in position with one hand, while turning the chuck clockwise with the other hand. Notice that the chuck's three jaws tighten around the shank of the bit. Keep tightening the chuck until the drill bit is firmly secured in place.
Place the end of the chuck key (for electrical cord drills) into one of the holes positioned around the chuck. Make sure that the teeth on the side of the key engage with the teeth on the side of the chuck. With the drill bit positioned in the end of the chuck between the three jaws, turn the key clockwise to close the jaws around the bit. Again, tighten the chuck until the bit is firmly secured in place.