Management companies are usually hired to maintain shared spaces and services of (mainly) apartment complexes or gated estates. The typical shared spaces and services that a Management company are responsible for can include lobbies, stairwells, lifts, main corridors, parking areas and green spaces around the complex. They are responsible for the upkeep ... of these areas as well as enforcing rules & guidelines to ensure that all open spaces and common areas are kept in order by all visiting and living in the building. Some rules can include: parking in designated areas, no smoking zones, low noise levels in common areas etc
All unit owners usually pay an annual maintenance fee / a service charge to the Management Company. If you a renter, good for you as you probably don"t have to pay Management fee, the Landlord more often than not pays this.
If you are not happy with your management company remember that they are only hired on a contract bases. Your complex probably has a residence committee so you should bring any issues that you may have to their attention.