Question

Heat can only move one way. What way is that?

Answer 1

Heat moves in three ways. Radiation, convection and conduction.

Answer 2

The only one way that heat can move is: From higher temperature
to lower temperature, never the other way.

Examples:
 
-- When you put an ice cube into a glass of warm soda, heat never moves
out of the ice cube into the soda, making the soda warmer.

-- When you mix cold water with warm water, heat never moves out of the
cold water into the warm water, causing ice to appear and the warm water
to get warmer.

-- When you blow your breath across a spoonful of hot soup, the soup
never draws heat out of your breath, chilling your breath and boiling the
soup on the spoon.

-- When you step into a warm steaming bubble bath, heat never moves
from your body into the hot bath, causing your tootsies to shiver and the
bath to get even hotter.