In this video Dr. Carlson does several experiments to illustrate how a vacuum works. A vacuum is created when all the air is removed from an object.
For the first experiment he connects two metal disks to a vacuum pump and puts the two disks together. The pump is turned on and the air is removed from between the disks. He then turns a valve to seal the disks shut, and now they cannot be pulled apart because of the air pressure pushing down. When the air is let back in, they come right apart.
Next he puts balloons in a bell jar and removes the air from the jar. Now the air inside the balloons pushes out, but with nothing to push back the pressure outside the balloons drops and the balloons break.
The next experiment shows how a vacuum can move water. He puts two jars attached with a tube inside a bell jar. One of the jars is full of water and has a small container of air attached to the top. When the air is removed from the bell jar the pressure inside the small jar presses down and forces the water up the tube and into the other glass.
Next he puts marshmallows inside a bell jar and removes the air. The air that is inside the marshmallows causes them to expand. When the air goes back in they return to normal size.
Finally he puts a bottle of shaving cream in the bell jar. When the vacuum is created the shaving cream begins to pour out of the container.