The Sphere (ball) emits an energy in all directions, providing a gentle surround for you. It may also be used to view past or future events. Think Crystal Ball.
The Square cut assists in grounding. Visualize the surrounding energies being drawn to the center of the square where the negative energy is transmuted into positive and released outward. It is very good for centering.
The Pyramids generally are four sided with a square base. They are used to focus the energy to a fine point. They are excellent for drawing off negative or blocked energies. They will enhance the property of the type of crystal used.
The Egg lends itself to reflexology or acupressure techniques. You are able to rebalance blocked areas as well as to hold them in your hand to remove stress.