Newbie question
 

I'm pretty new to the bonsai art, but i've read a lot of stuff about
taking care of a tree by now and i've seen a lot of pictures, i'm going
to collect lots of seeds this October and some of young, less than 30cm
trees i've spotted.

But i still have some questions, I've read somewhere that it is
possible to reduce the size of a tree of 2 meters to about 0,5 meters!
How is this done? I mean to do this it is needed to cut the main trunk
leaving the tree without any leafs, wont this kill the tree?

If someone could explain me, or point me some site with the
description of the technique i would be much gratefull.

Thanks very much, Joao Costa