What is the difference between the imperfect and perfect past.

The perfect past is like 'I ate, I sang' in English, and is used for an event that happened once and where the action was finished (eg 'I ate an apple, I sang a song'). The imperfect is for an action which is continuous, eg something you do every day. For example, I went to school every day for four years.
Direct comparison- which do you think is the imperfect and which the perfect?What did you do today? I played tennis.What did you do when you were younger? I used to play tennis.