Answer:
Big Brother, I mean, a HOA, is an acronym for a homeowners' association. The purpose of a HOA is to enforce the recorded covenants filed against the deed of your home and all other homes in the HOA boundary. They have the power to levy assessments, impose fines, provide services, and make regulations. They also maintain the roads (if they are private) and keep up the common areas (if any). The covenants that govern HOAs vary widely--ask your title company or HOA board for a copy of your covenants.
Another Answer
The association's major purpose is to operate the community as a private democracy according to the governing documents that are used to do so. Every owner signs a copy of the governing documents when purchasing property within the association. The volunteer board guides the association and yes, enforces the guidelines, and as well, is chartered by state law to protect, maintain and preserve the real estate assets that all owners own in common.
Most HOAs and condominium associations are multi-million dollar corporations, based on the value of the real estate.