Using the imperfect vs the preterite in Spanish (general use)

To talk about actions that took place in the past we can use both El Pretérito Imperfecto and El Pretérito Indefinido. 

Which one you need to use depends on whether you (or the speaker) consider the beginning and end of the action, or if you consider the action to be completed. This can be tricky for English speakers to understand because both tenses are usually translated the same in English.

Let's have a look at these examples:

In the first example where El Pretérito Imperfecto is used (abría) we can visualize a door in the process of being opened however in the second example where El Pretérito Indefinido is used, we can see a completely open door.

So the main difference between using these two tenses is:

Have a look at other examples in both tenses:

Trabajaba = we can see Susana working.

Trabajó = we can see Susana when she finished her work.

Corrían = we can see the boys running.

Corrieron = we see the empty corridors after the boys ran.

Comía = we can see Antonio eating his sandwich.

Comió = we can see Antonio throwing his sandwich wrapper away.

See also Using the imperfect vs the preterite in Spanish (time markers).