The document explains the past continuous tense and how it is used to describe actions that were happening at a specific time in the past. It provides examples of using the past continuous tense in sentences, such as "I was playing badminton at this time yesterday." It also discusses using the past continuous tense along with the past simple tense to describe two simultaneous past actions, like "Sam hurt himself when he was jumping over the vaulting horse." The document then presents an exercise in the form of a mystery about a murder where the past continuous tense is used to determine alibis and identify the murderer.