What is the difference between the perfect and imperfect tense?

There are two main past tenses that you will be using in French, the perfect tense (j'ai fait), the imperfect tense (je faisais), as well as the pluperfect tense (j'avais fait) which we won't be covering this lesson. To know which tense to use you have to think about the meaning you want to get across in English. For example, the imperfect tense is often used to express an ongoing action in the past (quand j'étais plus jeune, je jouais avec ma sœur - when I was younger I used to play with my sister). If, however, this was a one off occasion (or a completed action) e.g. I played with my sister yesterday, you would use the perfect tense, (Hier, j'ai joué avec ma sœur).

A useful method to remember which one to use is if you use the word was in English, you generally use the imperfect tense. For example, when I was younger (quand j'étais plsu jeune), I was doing my homework (je faisais mes devoirs) etc. 

Examples: I was eating an apple when my dad arrived (Je mangeais une pomme - imperfect - quand mon pére est arrivé - perfect)

I broke the window (J'ai casseé la fenêtre - perfect)

I used to like chocolate (J'aimais du chocolat - imperfect)