I don't understand charging by contact a neutral object and negatively charged rod.

Question

Please explain how to do charging by contact with a neutral electroscope and a negatively charged rod 

Answer 1

The leaves of an electroscope are made of conducting material.  Suppose they are neutral at the beginning.  When a negatively charged rod contacts the wire that feeds into the leaves, excess electrons from the charged rod migrate down into the leaves, and the leaves acquire a net negative charge.  Remember the excess negative charges on the rod want to repel away from each other, but have nowhere to go.  Contact with a neutral conductor gives them a path to migrate away from the rod, into the neutral conductor, building up a net negative charge on the conductor.