Step 1: Think of a real life example first.
Touch an instant cold pack when it activates, and it feels cold, that coldness is the surrounding area losing heat energy into the chemical reaction happening inside the pack.
Step 2: Translate that feeling into chemistry.
A reaction that pulls in heat from its surroundings to keep going is drawing energy in, rather than giving any out, and that is exactly what makes the surroundings feel cooler.
Step 3: Connect this to bond energy.
Whenever more energy is needed to break the reactant bonds than is released while forming new product bonds, the extra energy has to come from somewhere outside the reacting molecules, namely the surroundings.
Step 4: Name this behaviour.
A reaction that behaves this way, absorbing heat rather than releasing it, is called endothermic. \[ \boxed{\text{Heat is absorbed}} \]