Once you enter in Spain you need to make an appointment at the police station of your city, that is called “cita de huellas”. There they will give you a provisory NIE that will be exchanged in 40 days for your NIE card
The appointment shall be done through the website of the immigration office, completing the following steps.

• www.seat.mpr.gob.es
• Extranjería
• Cita previa de extranjería
• Acceder al procedimiento
• Provincias disponibles: Barcelona
• Cita Huellas

The required  document to get the NIE card are the following:

• Form EX17 form
• Passport (original)
• Passport copy of picture page, visa page and entry stamp page
• 1 passport picture
• Police appointment
• Domicile certificate (in case you have changed last year)
• Tax fee  number 790 (012)