Soldering is a joining process used to join different types of metals together by melting solder. Solder is a metal alloy usually made of tin and lead which is melted using a hot iron. The iron is heated to temperatures above 600 degrees which then cools to create a strong electrical bond. it is mainly used in PCB (PRINTED CIRCUIT BOARD)
There are also rosin-core solder wire which has a tube in the center of the wire that contains the flux. Lead solder wire is usually made from an alloy of lead and tin.