We use the Past Simple for completed actions in the past.
Here is a detailed list:
A. Things that are over / not recent
eg. My sister fell off her bike in 2010.
B. The situation now is different from the past
eg. I had a lot of anxiety a few months ago.
C. With a time marker (last year, yesterday)
eg. On Saturday, my friend and I talked for 4 hours.
D. Listing actions one after the other
eg. First we went to the beach, then we ate at a restaurant, and then we took some pictures.