Everyone who works or lives in the Netherlands is obligated to have a health insurance. All the basis needs for health care are covered in this the basic insurance. You can extend the basic health insurcance with an additional health insurance to cover more medical care.
Every insurer offers a basic healthcare package, but they do differ in the premium you will have to pay. This is why ZorgKiezer.nl compares all of the insurances and tries to prevent you from overpaying.