about the force

the force is some kind of energy the Jedi and other force sensitive living forms can use for feeling things and people and moving things just with their mind. Obi-Wan Kenobi describes it as "an energy field created by all living things. It surrounds us, penetrates us, and binds the galaxy together." In Star Wars Episode 1 we learnt that the ability in using the force depends on the midi-clorians (some kind of micro-organisms) in your body.
The most important users of the force are the Jedi who try to help the galaxy staying "good". They work with the light side of the force. But there are as well people like the Sith and the Dark Jedi who use their ability in the force for destroying others and their personal wishes - they get their power from the dark side of the force.