If you are an International student and you do not have a Danish social security number (called CPR-number), you need to register at ITU in order to get your ITU-login. You do this at the IT Department.
As you need your ITU-login for a number of things, e.g. your ITU-email, we advise you to come by the IT Department as fast as possible after arriving in Denmark.
Remember to bring valid photo identification, e.g. your passport.