The passato prossimo can have a few different meanings: Io ho mangiato could translate as “I have eaten,” “I ate,” or “I did eat,” depending on the context. The imperfect tense is a simple tense, formed by a single word, that is used to express a habitual or ongoing action in the past — for example, I used to go swimming at the lake. The imperfect actions are clearly happening in the past. We know that it used to happen, or that it was happening, but we don't know when the actions were brought to an end.