so the imperfect is used when an action is repeated ( for example "we fished during the summers") for one thing. It is also used for weather and telling time, like "tenía calor" or "eran las tres". Another thing is describing characteristics in the past, like saying someone was short or nice. Also, the imperfect is used for thoughts, feelings and beliefs unless they are extremely brief, where the preterite should then be used. Or, if two things happen at the same time the imperfect is always used. The final use is for narrating a story in the past. the preterite is only used for actions that happened once and never happened again, for example "he walked", not "he walked many times".