Chemistry -> Thermochemistry -> Exothermic reactions
As it was asked to give an example of an exothermic change, let's first think of what is the meaning of exothermic and endothermic.
An exothermic change or reaction is characterized by releasing energy to the surroundings, usually as heat.
An endothermic change or reaction is characterized by absorbing energy from the surroundings.
For example:
If we dilute a strong acid, such as sulfuric acid, in water, we are able to feel the container getting hotter and hotter. That means the reaction happening between the sulfuric acid and water (dissociation) is releasing heat to the surroundings.
And if we mix two compounds and feel the container getting colder (dissolution of KCl in water, for example), the process is endothermic, because the reaction is getting heat from the surroundings.
Now that we know the definition, a simple example can be thought of, keeping in mind that the main characteristic of an exothermic change is the release of heat:
Combustion is an example of exothermic change/reaction since it is generating heat and most of the times even fire, like when we lit a bonfire.
When we lit a bonfire, an exothermic change occurs as the wood reacts with oxygen and produces fire (heat).