How do endothermic and exothermic reactions differ?

Endothermic reactions take in heat from the surroundings, whereas exothermic reactions release heat to the surroundings. Exothermic reactions release heat as the energy released from the bonds being made in the product(s) is more than the energy taken in required to break bonds in the reactant(s). Breaking bonds requires energy as an electrostatic attraction must be overcome, whereas the opposite can be said for bond formations - energy is released as the atoms share electrons and the bond is formed.