The Jedi Order was an exclusive club/cult that worshipped the Force. They could lift rocks and move boxes while standing on their heads. They also loved chopping people's bits off. Most Jedi lived at the Temple on Coruscant, except when they died.
Height of the Jedi
Stuff was cool, Sith were dead!
Fall of the Jedi
For 1,000 years, the Sith lay dormant while plotting against the Jedi. Finally, Darth Sidious came into power as the Chancellor, Palpatine. He secretly arranged for a Seperatist movement to start a civil war, which ultimately led to the Galaxy turning on the Jedi and supporting his move to wipe them out. It didn't help that the Jedi Order was by this time composed mostly of total morons who couldn't even recognize a Sith Lawd when he was literally 2 feet from them. Except for a few lucky individuals who escaped to EU system, and a couple from the OT, the Jedi were annihilated.
Return of the Jedi
Luke Skywalker made a new Order after the fall of the Empire. He made many changes, like marriage was okay now. He was the only one who supported the idea of being allowed to marry your sister though. His descendants made a royal mess of things, though.
Taken as babies, younglings were raised in the Jedi Temple on Coruscant and taught the ways of the Force by Yoda.
When a Jedi reached their early teens, they were assigned a personal master and became a Padawan learner.
Once their apprenticeship was finished, the Padawan then hopefully completed their trials and were promoted to full fledged Knight.
Only a Master could train a Padawan, and were the most experienced and wisest of the Jedi Order.