Answer:
Association fees are established every year -- usually, based on last year's expenses. Once the budget is finalized, owners receive details about the new assessment amount, which owners are required to pay, usually on a monthly basis.
Assessments cover the expenses of operating the community, and may pay for landscape work, utilities, garbage pick-up, master insurance policy premiums, preventative maintenance, contributions to reserves, and more.
You can ask for a copy of the budget if you are an owner, and your treasurer can explain each line item for you.