The Past Continuous Tense is used to describe actions that were ongoing in the past. It is formed using the past tense of the verb "to be" (was/were) followed by the present participle (the -ing form) of the main verb. For example, "I was reading" indicates that the action of reading was in progress at a specific time in the past. This tense often sets the scene for other actions that occurred. For instance, in the sentence "While I was studying, my friend called," the ongoing action of studying is interrupted by the completed action of the friend calling.