There exist many different modelo´s 790, the one we supply here is for the homologation of titles obtained abroad.
From this website:
http://www.mecd.gob.es/educacion-mecd/areas-educacion/sistema-educativo/gestion-titulos/estudios-no-universitarios/titulos-obtenidos-fuera-de-espana/convalidacion-no-univ/abono-devolucion-tasas.html
Scroll down to ´descarga del Modelo 790´ with the pdf file symbol next to it. Press that link to download printable form that comes in triplicate, with a unique ´numero de justificante´ in the top part of the form. Your bank needs this number to process the form.
Take all copies to the bank, pay, they will keep one copy. Bring other two to relevant authority as proof of payment. They will keep one as well. Remaining one is for your own administration.