A good beginners weight for an average man with the KB is 16kilos - or 35lbs.
You can work up to the bigger ones.
All these slow presses that people do? They can easily be done with dumbells. The KB's are a piece of kit mean't for different exercises. They have a handle at one end so you can swing them about!
This shows some of the basics
http://www.youtube.com/watch?v=Lwme8rkzetg