This can be used for online banking, changing information at public authorities and much more, e.g. signing up for childcare or correct your taxes.
You can obtain a NemID if you have reached the age of 15 and have a Danish social security number (CPR number). To get a NemID you should contact your local citizen service centre or your online bank. Remember to bring a valid ID.
When you have obtained a NemID you will receive a key card as shown on the picture below.
This contains three pages of different codes. You must use this with your login information when you have to use different internet services securely.
Read more about NemID.