SimCity 4 > Civic Services
You can get by without civic services and amenities when you start out. Soon, however, your sims (through the advisors) will clamor for them.
For each service the starting cost is fixed, but the monthly costs are adjustable. For a safety service, there is one monthly cost that sets the radius of effectiveness. For health or most education services, the two monthly costs determine the reach of the service and the number of people working for that service. Some education services have a fixed reach, and their monthly cost decides their effectiveness only.
Be sure you don't spend less than the service needs. Otherwise, you will find yourself with striking teachers, doctors, cops or firefighters, with a resulting dip in mayoral ratings.
Parks are included with the services, even though their monthly cost is fixed. Recreation is also a service that draws sims to your city by making it more pleasant.