There are two prerequisites for Free Running: 1. be too broke to own a skateboard like a proper hoodlum, and 2. listen to shitty noise which passes as punk these days.
Of course, others are a bit more balanced in their description of this utterly ridiculous fad. In fact, if you want to learn how to get started acting like a semi-acrobatic epileptic, then WikiHow is your place....
So you want to get started in Parkour or Free running. The videos are out there... people doing insane jumps between buildings, over railings and through cities. These trained experts are probably practicing either parkour or free running. Parkour is a form of movement that stresses efficiency and speed. The point is to to get from spot A to spot B as quickly and efficiently as possible. Free Running is similar but it also involves aesthetic movements such as flips, spins, and many other forms of 'flair' (traceurs, practitioners of parkour, usually frown upon movement "wasted" on aesthetics). Also, Free Runners usually don't have a set path.
Remember, kids, Free Runners don't have a set path, because purposeful motion kills your buzz and is an affront to the whole concept of being an idle loser.
Again, France...this is why people in the productive part of the Western world hate you. Those of us in the part of the world not noted for being surrender monkeys just say "what the fuck is wrong with you people."
*Or, if you're really a pretentious douche, Parkour.
** Did I mention that's really, really lame..."The art of motion"? Le Ghey.