Past Simple -> actions finished in the past (signal words such as yesterday, in 2001, last year etc.; > 3 actions in the past = past simple)
Present Perfect -> actions started in the past + are still going on; recent action; focus on result (when = not mentioned nor important)
Past Continuous -> longer action in the past (could be interrupted by shorter action; could be going on at the same time) or description of sth. in the past (the birds were singing happily, and we were enjoying our ice creams)
Past Perfect -> earlier action in the past (signal words: before/after)
Used to/didn't use to -> habits/repeated actions in the past