Conduction
Conduction is how heat moves through a solid object from the hot end to the cold end.
Think of it this way
A metal spoon rests in a bowl of hot soup. The end in the soup gets hot first. Heat then moves up through the metal toward the handle, one part at a time. After a few minutes, the top of the handle feels warm even though it never touched the soup.
Explaining conduction by grade level
Touch a metal spoon in hot soup and the handle gets warm. The heat travels through the metal from the hot end. Some things carry heat well, like metal. Other things, like wood, do not carry heat as fast.