The preterite is used to explain something in the past which has a definite beginning and ending such as ‘Ayer, fui a la playa’ meaning yesterday I went to the beach. The time phrase indicates that the action enclosed within a specific date. The imperfect is used to describe a continuous action in the past such as ‘cuando era joven, jugaba fútbol’ meaning when I was younger I played football. This is a continuous action that doesn’t have a specific beginning or end.