For a newcomer one thing to be careful of is squeezing the tweezers too hard when holding a small part, quite often the part will 'ping' off at great speed involving much searching. Basic stuff, but you don't always think of it at the time.
Hi Clockboy has explained it very well. The K&D tools work well enough in the demonstrations if used properly, I would advise watching a few of these on The tube just to get familiar with its use. The method is that when fitted tio the staking tool and screwed down it supports the arms of the balance on to the stake avoiding distortion. Watch the videos before having a go.
You can also do this...
You buy a pocketwatch movement on Ali:
It's a ETA clone, and practice on this one... It's a bit bigger than a normal movement.
After your done, and when it's still working, you assemble it in a case, and were it proud, your first on build watch!