Many official organisations and businesses in the Netherlands require you to use a digital signature called “DigiD” in order to access their online services. To get DigiD, you must first acquire a username and a password. With these, you can sign in and access personal data or submit forms digitally.
Much of the information about DigiD is available in English, but the online application form is in Dutch. For internationals who have trouble understanding this form, there is a step-by-step application guide in English available on https://www.iamsterdam.com/en/living/everyday-essentials/finance/digid. The guide shows a picture of every screen and explains what you need to fill in and where.