Kid, I've flown from one side of this galaxy to the other. I've seen a lot of strange stuff, but I've never seen anything to make me believe there's one all-powerful Force controlling everything. No mystical energy field controls my destiny - it's all a lot of simple tricks and nonsense.
Han Solo in A New Hope
In the Star Wars universe, the Force is an energy field produced by all living things, enabling certain people with psychic powers such as telekinesis and precognition. The true nature of the Force is never fully explained, although it is reduced to technobabble by the introduction of Midichlorians in later movies.
The Force can be used in different ways, for good or evil; the Force has a two sides, light and dark. The light and dark sides of the Force are the Yin and Yang of Star Wars. A Jedi uses the Force for knowledge and defense, never for attack (although the Jedi Mind Trick is acceptable). Fear and hatred are the allies of the Sith, followers of the Dark Side.
Which side is stronger? Jedi Master Yoda's point of view is that the dark is not:
YODA: A Jedi's strength flows from the Force. But beware of the dark side! Anger, fear, aggression - the dark side of the Force are they. Once you start down the dark path, forever will it dominate your destiny, consume you it will, as it did Obi-Wan's apprentice.
LUKE: Vader. Is the dark side stronger?
YODA: No. Quicker, easier, more seductive.
Whether this is true, or if the light side is any stronger than the dark side, remains to be seen. Battles with the force and lightsabers between Jedi and Sith have had varied outcomes. Furthermore the light and dark distinction could be meaningless construct - as Hamlet says, there is nothing either good or bad but thinking makes it so.
May the Force be with you.