What are the differences between the perfect and imperfect tenses?

(Apologies, this keyboard doesn't allow some accents)Firstly, the perfect tense requires an auxiliary verb: avoir or etre. Then the past participle is added, e.g. j'ai bu - I have drunk/I drank. The imperfect requires a specific set of endings - -ais, -ais, -ait, -ions, -iez, -aient - which are to be added to the imperfect verb stem, e.g. je buvais - I drank/I used to drink/I was drinking.Secondly, the general rule about the perfect tense is that it describes an action that has finished, that has only been done once, all in a specified time. An example of this is 'hier j'ai joué au foot' - football is the finished action, and 'hier' specifies the time in which this action was completed. The general rule about the imperfect is that it describes an ongoing, repeated or continuous action, in an unspecified time. E.g. 'quand j'étais jeune, je jouais au foot' - the football was done during the subject's childhood, not on a specific date, and we aren't sure of how long they did this. It is known that they don't do it anymore, as the imperfect generally implies that they used to play football. At GCSE level, this is what is required but in A Level, you learn when to use them together and which component is which.