The Jedi Council is the governing body for all Jedi so to speak. The Jedi are practioners of the Force which use the power that they harness from it for the benefit of the people and races of the galaxy that is far far away. The Jedi Council played a pivitol role in the prequel films but because they were destroyed by the Sith at the end of the star Wars III - Revenge of the Sith, they never appeared in the original films.
The most senior member of the Jedi Council was Mace Windu who was blasted into the air on Coruscant by Palpatine after Anakin Skywalker who had chopped off Windu's hands when Mace wanted to arrest Palpatine. Anakin had been given a seat on the Jedi Council but was not awarded the title of Grand Master which annoyed Anakin and further pushed him into the hands of Palpatine.
The force was first discovered on the planet Tython, a planet in the deep core of the galaxy to the "north". The planet doesn't feature in any of the films but it could be best described as being like Alderaan which itself only appeared briefly in the films.
There are two sides to everything and the opposite users of the force are known as the Sith who use the force for their own powers. Whereas the Sith only numbers two, a Master and an apprentice, the same command doesn't exist for the Jedi.
Force practitioners are able to come back as "Force Ghosts" when they die if they are able to know how to do it. After Obi-wan Kenobi was killed by Darth Vader, Obi-Wan was able to come back immediately and provide guidance to the young Luke Skywalker.