We use the past progressive tense to talk about an action that was happening at a specific time in the past. The form for the past progressive is:
subject + past tense be verb + verb (-ing)
• Use the past progressive with action verbs, not with non-action verbs such as senses (see, hear), emotions (love, hate), possession (have, own), and mental states (think, remember).
• Use the past progressive tense for an action that was happening when another action interrupted (stopped) it.
• If you are discussing two actions, the first action is in the past progressive tense and the second action is in the simple past tense. (I was watching TV when you called)