DigiD (short for Digital Identification) is a form of online ID that allows you to access many services and government websites in the Netherlands. The DigiD consists of a username and password that are linked to your personal public service number (BSN). You need your DigiD to do your administration online in the Netherlands. You can apply for your DigiD on the official DigiD application page(opens in a new tab). Once you have your DigiD it is recommended to download the app on your phone, as often logging in to official websites requires you to verify it via the app.
Read more about DigiD here(opens in a new tab).