What is the difference between the preterit and imperfect tense? When would each be used?

Preterit to express an action completed at a definite moment in the past Eg. Yo estuve en su casa por tres horasto express actions that because of their nature are not usually repeatedEg. El hijo de Antonio nació en ese hospital Imperfect to describe actions that took place on a regular basis or that were habitual or customary in the pastEg. Yo veía a mis primos todas las semanasto describe people or states of indefinite duration in the past with no reference to its beginning or end Eg. su esposa era altoEg. Nosotros estábamos muy nervioso