Heat is a type of energy. It spreads from warm things to cold things. The moving molecules pass the heat along. For example, you can notice this fact if you put butter on your toast. Heat passes from the toast into the butter and causes it to melt. Altough a piece of bread is solid, it has molecules which move. When the bread is toasted, these molecules move faster.
Cold butter also has molecules. As they are cool they move very slowly. The motion passes between the molecules until the butter becomes soft and warm. The ice cubes have very slow-moving molecules. Because the ice-cubes are very cold. On the other hand, the fruit juice has molecules with more heat energy which move faster. If we put ice in a glass of fruit juice, the molecules lose energy and move more slowly. The juice stays cool until all of the ice melts.