What is the difference between the Preterite and Imperfect tense?

Preterite: Refers to actions which took place and were completed at some point in the past. In this context it may be accompanied by time phrases such as 'ayer', 'el lunes pasado', 'hace una semana' etc. In a narrative context, it is often used alongside the imperfect, with the preterite signalling a completed action or series of actions and the imperfect providing the description. It also may refer to an action which was completed before another took place or to one which was interrupted at some point in the past. Imperfect: Refers to an ongoing state or action in the past whose beginning or end is not specified. In this context, English normally uses the simple past or a construction with ‘used to’. In narrative, it is used with the preterite where the imperfect provides the background description for the actions expressed by the preterite. In English, both correspond to the simple past. Generally, it refers to habitual past actions. It is can also be used in place of the present tense to request something in a polite way eg 'I wanted to speak to you'.