Welcome to a beginners rough guide on beginning your Parkour training.

Firstly to practise Parkour you must have basic motor functions and strength,
nothing else is required apart from maybe some running shoes if you don't want to go barefoot (some do train like that).
Anyway, to begin with you need to break down each of the different ways of moving,
this can easily be done by using Georges Hébert's 'Méthode naturelle' as a guide, in this he explains that human movement is compromised of;

Walking
Running
Jumping
Climbing
Quadrupedal movement (crawling)
Balancing

With this as a guide you can build usefull skill
and you can see that these are the things you must train to be able to
practise parkour as parkour is the art and discipline of efficient human movement.

With that in mind I will list below the basic movements and techniques found
to be most efficient and usefull in Parkour and which must be trained constantly
to the point at which they become as familiar as walking.

Running
Jumping (standing, precision and running)
Crawling
Rolling (a safe painless roll diagonaly accross the back)
Vaulting (any passement over an obstacle that is fast, simple and safe)
Balancing (walking, standing, running and crawling)
Catching Yourself (from a jump or from a fall)

There are many tutorials and guides for beginners but the best at the moment
that I have found is linked below which includes links to videos and detailed walk-throughs.

http://worldwidejam.tv/pkbasics.1.jam.parkour.html

Also the best forums for parkour have to be http://parkour.net which have many experienced people on hand to help.