In English this means: Jorge and Margarita got married last Friday. The verb in the sentence is conjugated in the preterite because it refers to a concrete action that took place in the past, in a precise moment in the past (last Friday). The imperfect, "casaban", would be incorrect in this context since the imperfect is used for actions in the past that which beginning or end are imprecise, or that aren't finished or that were interrupted by some other action in the past.
