The Dutch healthcare system is referred to as a ‘gatekeeper system’: the General Practitioner (huisarts) or family doctor being the main link to any specialist or hospital. You will need to make an appointment with your GP to get a referral to see a medical specialist at the hospital.
Health insurance is compulsory for every person who lives or works in the Netherlands, although there are a few exceptions (e.g. Phd students). You can check if you need health insurance at Zorgverzekeringslijn.nl. You can be fined if you do not get insurance when required.
Insurance reimburses a part of your medical expenses, depending on the level of coverage you have chosen. You may also opt to take out additional insurance to cover costs not included in the basic package.