Do you drink coffee? Does it help you wake up? Focus? Give you an energy boost? These are some functions (purposes) of caffeine. Or do you avoid it because of the energy crash, acidity, or jitteriness it causes you? These are some dysfunctions of caffeine.
Looking at society from a functionalist point of view includes examining how something is functional (useful) and dysfunctional (not useful).
The structural functionalist point of view sees society as a complex system whose parts work together to promote stability. The human body is often used as an analogy for structural functionalism. Many different parts (heart, liver, brain, lungs) work together in order for the body to work.
Functionalism is also focused on maintaining harmony in society, just as your body works to maintain harmony (if you are cold, your body shivers to warm you up, if you are hot, your body produces sweat to cool you down).
When we look at terrible occurrences such as the mass shooting in D.C., we will immediately see many dysfunctions caused by this horrendous crime. Families have lost a loved one, provider, and support mechanism. Our Navy has lost valuable members of their workforce, and many surviving members may suffer from depression or post-traumatic stress disorder. The members of society as a whole feel disheartened, fearful, and confused by these horrific acts of violence. Looking at the negative consequences of a behavior is part of structural functionalism.
Functionalism also analyzes how criminal acts can provide some functions in society. (This does not mean justifying atrocious acts of violence against innocent people in any way). Crime can have a role in society, and some positive outcomes can be seen coming out of extremely negative circumstances.