When I was taught about it, my teacher said that passé composé is when an event has occured once in the past. Kinda like, you started something but it ended too. For example: "I ate a banana" "I went to her house on Sunday" Whereas, Imperfect tense is used while saying something you did regularly or repeatedly over a period of time. For example: "I used to work there" "I was learning French for 3 months" That is how I remember it. When using Passé it's sort of like describing something you started but it ended at the same time; whilst Imperfect shows more of the continuous side; if you know what I mean. Hope this helps! :)

"je les confonds toujours"