What is the difference between the preterite and the imperfect tense?

Spanish has two past tenses: preterite and imperfect. Most verbs can be put into either tense, depending upon the meaning. Generally speaking, the preterite is used for actions in the past that are seen as completed. Therefore, use of the preterite tense implies that the past action had a definite beginning and definite end.Eg:Juan habló con la estudiante.Juan spoke with the student.(here there is an implied beginning and end even though the exact time the conversation happened and the length of time it lasted for are not specified)The imperfect tense however, is used for actions in the past that are not seen as completed. So, use of the imperfect tense implies that the past action did not have a definite beginning or a definite end.Las chicas hablaban en inglés.Eg:The girls used to speak in English.(there is not a definite beginning or end, this was an ongoing past event)