For actions that did not have a definite beginning or a definite end.

For actions that "set the stage" for another past action.

For actions that can be viewed as single events.

For actions that occurred during a specific period of time.

For actions that were part of a chain of events.

To describe a mental state in the past.

For stating one's age in the past.

Ongoing actions in the past.

For telling time in the past.

To describe "incomplete actions” in the past.

To indicate the beginning or end of a process.

To describe completed actions in the past.

To describe the characteristics of people, things or conditions.

To give background information in the past.

To give the time, date, weather, or season in the past.

To refer to habitual past actions.

The action following "mientras".

The common expression "el otro día".

Was-ing and were-ing

Expresses a series of completed events.