Badi Related

Hi

I have come across so many badi's ,i know the need of the badi's ,but i dont know the procedure to implementa badi,what are the components of a badi.?.when do we know that a Badi can be used at a particular point..?

what knowledge should be required for a Functional Consultant realted to Badi's..up to what extent she should know..?

Any doc related to Badi's with a small example would surely help a lot...if any one have related docs kinldy mail to me at sanjana_priya22@yahoo.co.in

regards,

Sanjana