We use the Past Continuous to =describe actions that were ongoing or in progress at a specific point in the past or over a period of time in the past=. This tense indicates =actions that were happening at a particular moment in the past, or actions that were in progress when another action occurred=.
Form: was/were + V+ing
For example: "She was reading a book when the phone rang." This sentence indicates that the action of reading was in progress when another event (the phone ringing) interrupted it.
Signal words: ="while", "when", "as", "at that moment", "at that time"= etc.
The Past Simple is used for completed actions or events that occurred at a specific point in the past, while the Past Continuous is used for actions that were ongoing or in progress at a specific moment or over a period of time in the past.