There are two types of NIE for EU passport holders. You can get a NIE number or a NIE card. A NIE number is simply a number written on a white piece of paper. The NIE card is a small green card, also called a residence certificate (Certificado de Registro de Ciudadano de la Unión) or a resident card (tarjeta de residencia), which will allow you to complete all the necessary documents for everyday life in Spain. This residence certificate is equivalent to the NIF (identity card for Spanish citizens).
As well as bringing these forms and documents, you will also need to pay a state fee (€9.84 for a NIE number or €12 for a permanent NIE card) before you receive your official documents. Payment can be made either in cash or by direct debit from your current account.