Your “apellido” is your last name. However, last names are done very differently in Spain. Everyone has 2 last names and when you marry your last names don’t change. Confusing? At least for us Americans it is! I’ll try to illustrate how it works using some made up names:
Juan Rodríguez Fernández
Juan is the given name. Rodriguez is the Father’s first surname and Fernandez is the mother’s first surname. Now to continue the illustration, let’s pretend that Juan marries:
María Gómez Martínez
María last name follow the same pattern as Juan’s and she will always have Gómez Martínez as her last name. There is no saying, “We’re going to the Smith’s house tonight!”, because there are now 4 last names involved. To finish the example, let’s say that Juan & María have a a son:
Rafael Rodríguez Gómez
Do you see? The son’s first surname came from his father while his second surname came from his mother. So the child’s last name does not match either of his parent’s last names and now the house has 3 last names in it!