Temperature is how we define the average amount of movement in all the atoms or molecules in a material.

Things that are hot have atoms that mostly move very fast and things that are cold have atoms that are mostly moving slowly. Not all the atoms are ever moving at the same speed though. For example, in a gas, molecules can speed up or slow down after bumping into another molecule (trying following one ball in this video:
watch here , and think of each ball as a molecule in a gas. It changes speed pretty often!). The heat of this gas depends on the sum of all the speeds of every molecule in the gas.

This means that heat depends on how many molecules you have too.

Temperature, on the other hand, only cares about how fast most of the atoms are moving so it doesn't depend on how many molecules there are. To change the temperature of a gas, or anything else, you have to add or take away heat, which makes the molecules move faster or slower.