Endothermic reactions absorb heat and get warmer (End Up).
Exothermic reactions lose or release heat and get colder (Exit down).
To test this out, look at a whack-a-pack and make observations. The pack starts off at room temperature and when you hit it, the reaction occurs. This is a chemical reaction for a few reasons - one you can hear it fizzing. Two it blows up so a gas is being formed (1 of the 4 ways you know a chemical reaction has occurred). And Three there is a temperature change (another of the four ways). The pack gets really cold which means it is releasing heat and this is an exothermic reaction.
Watch this little video to see how it works. These are available at Dollar Tree at Valentine's Day if you are interested.