ELI5: Explain Like I'm 5

solder

Soldering is like sticking two pieces of metal together. A soldering iron is a special tool which is heated up to a high temperature and then used with a special type of metal that melts at this temperature. This melted metal, called solder, flows into the joint between two pieces of metal, joining them together. Soldering is useful for making electronic circuits, joining pieces of metal together for jewelry, and even for fixing small objects like toys.