You can only apply for a DigiD if you are a resident of the Netherlands. To apply for your DigiD, you will need a Citizen Service Number (Burgerservicenummer - BSN), which you will receive at your registration appointment.
You can apply for a DigiD for free on the DigiD website. The online application form has 3 steps and is in English. Make sure to fill out the exact address you are registered. After filling out the application, a validation letter will be sent to your home address within 1-2 weeks to prevent fraud.
Municipalities Voorschoten and Wassenaar offer their non-Dutch speaking European citizens services and e-forms in the English language with their eID.