What is the difference between the perfect tense and the imperfect tense?

The perfect tense (in french le passé composé) is used to describe completed actions, whereas the imperfect tense (l'imparfait) refers to an event that used to happen, or an action that cannot be described as 'completed'. A common use for the imperfect, especially at GCSE level is to describe about something you did when you were younger. For example, If I want to say 'when I was younger I used to watch television' I would use the imperfect tense - 'quand j'étais plus jeune, je regardais la télévision.' If I wanted to say 'I was watching television when my mum came home' I would also use the imperfect tense, as I am describing an action in the past but that has not been fully completed - 'i was watching it' I did not 'watch it.' So, 'je regardais la television quand ma mere est revenue.' You can identify the imperfect tense from its ending - '-ais, -ais, -ait, -ions, -iez, -aient.' The perfect tense is a compound tense, meaning that it uses the verbs 'avoir' (to have) or 'etre' (to be) to form it. We have this in english as well when we say 'I have eaten' or 'I have watched'. As I said before, this tense is to be used to describe completed actions. 'I ate an apple' (j'ai mangé une pomme) uses the perfect tense as the apple has been eaten - it is an action that has finished.