1. The Imperfect tense
The Preterite tense is used to describe an event that took place at a specific time in the past: John went to Mexico last year. We ate a large meal.

2. The Imperfect tense:
A. describes an action that was repeated [always, used to, usually, etc]
John visited (used to visit) Mexico every year.
We ate a large meal every Sunday.

3. Carlos always spent his vacations in Mexico
Carlos always spent his vacations in Mexico. but last summer he spent it in Puerto Rico. On Saturdays I played tennis with Bob, but last week I played tennis with Tom. Generally, I got up early, but yesterday I got up at 10:00

4. B. describes an action that took place over a period of time:
I was in Spain for two months last year.
Ana spent three weeks in Argentina.

5. C. describes someone or something in the past (sets a scene): Paula was not happy. It was cold in the mountains. She had blue eyes. It was 2:00 when he arrived.