Spanish:: PRETERITE and IMPERFECT..?

Preterite verbs indicate an action that happened and then ended(in the past) and imperfect verbs indicate an action in the past that happened for a period of time. example: Ayer cuando caminaba(imperfect) hable (preterite)con ella. you use the imperfect"caminaba" to show that it was happening for a period of time, you use "hable" to show that it happened and then ended.