how would i make a vanndagraff generator?

Question

and how does it work

Answer 1

They're a very big pain--any static electric generator is, because the standards of craftsmanship must be very high or the thing won't work.

The belt gathers charge from the low end of the machine and the comb in the dome scrapes it off the belt. The charge accumulated on the dome raises its voltage until the air around the dome breaks down.

The best source for this sort of thing is the 'weird science' website run by Bill Beaty, note the spelling. Do a google search. His stuff works well, and there are multitudes of projects in there.

Answer 2

Try this source.