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IN SUMMARY:
For exothermic reactions as the energy of products is lower than reactants, heat is released.

For endothermic reactions as the energy of products is higher than reactants, heat is absorbed.

"Bond-making" processes are exothermic.
"Bond-breaking" process are endothermic.

The heat change in joules for a process can be calculated from the temperature change of the surroundings - for example the water in a bomb calorimeter or in which a reaction is being carried out.

q(system) = -q(surroundings)

The heat change of the surroundings depends on its specific heat capacity, C [the amount of heat required to raise one g one degree Centigrade (Kelvin)], the mass of the surroundings and the temperature change.

q = m × C × ΔT (g × J g^-1 K^-1 x K)