Condo or condominium fees are only generally only applicable to buildings which are shared or broken up into multiple dwellings. A condominium building is the most common use case where you will see condo fees applied. Condo fees go towards repairs, maintenance, management and other general upkeep of the building and it's environment. A portion of each months condo fees will also go towards a contingency fund for future repairs or a rainy day.
It is the responsibility of the owner to pay any applicable condo fees on time to ensure they don't incur penalties or other potential legalities.