What is the difference between the imperfect and the preterite tense in the past indicative?

Whilst both the preterite and the imperfect express actions that have happened in the past, their uses vary significantly.The preterite is used to describe actions that have happened one time, a closed and completed action. For example: Yesterday I went shopping=ayer, fui de compras or last week I went to the cinema=la semana pasada fui al cine.However, the imperfect is used for habitual actions, that kept happening in the past (repeated actions). For example: When I was younger, I used to play games=Cuando era más joven, jugaba juegos. The imperfect is also used to describe, for example: There were many people on the bus= Había mucha gente en el bus.