When animating a scene, you will often have to animate a character interacting with props, such as grasping a cup of tea, a sword, a gun, or a flower bouquet. These props are not part of the main rig, but you need a way to control them easily.
Let's imagine a scene where our character finds a giant diamond and picks it up with his left hand.
006-Props.blend. It has our character Otto in front of a stand with a big diamond on top. The character has a very basic animation with three Extreme positions defined to pick the diamond with his left hand. The next screenshot shows the first keyframe: