De: Possession, and Contraction

 La Posesión (possession)
In Spanish, possession is expressed by the word de (of). There is no 's in Spanish as there are in English.

 El dinero de Carla.                   It's Carla's money
Son los abuelos de Pablo.      They are Pablo's grandparents.
¿De quién es el coche?          Whose car is it?

Una contracción (a contraction)

A contraction is the joining of two words that may also be said or written separately. In English contractions are optional, but in Spanish there are only two contractions. They are obligatory: De and el contract to del, and a and el contract al. Not other articles contract with de or with a.

Es la casa del maestro.                         It is the teacher's house

Es la casa de los maestros.                 It is the teachers' house
Es la casa de la maestra.                      It is the  (female) teacher's house.
Llego al mercado a las dos.                 I'll get to the market at two.
Llego a la tienda a las tres.                   I'll get to the store at three.