Structural Functionalism is one of many schools of thought in the field of sociology. It presents the construct of society as a great organism, composed of many groups and demographics that, in their interactions with each other and with themselves, keep “The Machine” that is society operational and prosperous—functional, if you will.
These groups that comprise the organs of the organism are defined by many different metrics, and often overlap. Wealth, employment status, size of family and criminal activity are just a few examples of defining attributes of these groups.
It’s important to note that the “bad” parts of society—homelessness, crime, riots, etcetera—are (through the lens of functionalism) just as integral to the regular operation of the Machine as the rest of society. Crime employs police officers, homelessness brings charities to local and accessible urban areas, and the threat of protest or riot keeps politicians on their toes. Furthermore, the presence of the counters to these problems (police, charity etc) bring an unquantifiable morale boost to the populace in the form of visible reminders that functionalism is being maintained.
Structural Functionalism is why society functions the way it does. By emphasizing the relationships between the various social institutions that make up society like government, law, education, and religion.
Example in my life- Is the structure I have in school because the school provides education for me and then will teach me how to pay taxes. That will go to state taxes which keeps the state running.