Once Residence Permit interview is complete.
You will receive a mail from Finance Department ,
It will contain a 11 digit number called Identifikationsnummer.
Next you need to login to register for tax filing . Use the below link
After submitting the form,
You will have to acknowledge the link received in email.
After acknowledgement , you will receive another email with your login id and an activation id
You will have to wait for another id that you will receive by post.
With both the documents, you can complete registration for tax filing .
The financial year is the same as calendar year.
nrw tax link link