Confusion about usage of imparfait

Question

If I am recalling something from the past, do I need to use PC or imparfait?

For eg: I got down from the train that day.

Je me suis descendu du train ca jour

OR

Je descendais du train ca jour?

Which one is correct?

Accepted Answer

The answer is "it depends".
We need to see the complete context to work out whether it is more appropriate to use the imparfait or PC.
If this was a sentence in a story where you were talking about something you habitually did every day (i.e., getting off the train), then the imperfect is appropriate.
If you are describing a specific one-off event (the main story line) then PC would be better.
Generally speaking, imparfait sets the scene, and PC describes the action.
I'm a non-native speaker and PC v imparfait is a continual battle I'm afraid!