"I was reading that book last night."
Translation:wa'Hu' ram paqvetlh vIlaDtaH.
That's an excellent question and one that this course is not well equipped to deal with. The -taH suffix does indicate "continuous aspect". Klingon does not have tenses so it could be past, present, or future. As stated in The Klingon Dictionary:
Klingon does not express tenses (past, present, future). These ideas come across from context or other words in the sentence (such as wa'leS tomorrow). The langauge does, however, indicate aspect: whether an action is completed or not yet completed, and whether an action is a single event or a continuing one.
The -taH suffix is the method by which the language indicates that an action is ongoing. I will admit that the continuous aspect does not line up exactly with the use of the progressive tenses in English. However, to keep things simpler in this course which does not use context, we have equated the Klingon continuous aspect with the English progressive tenses. Thus vIlaDtaH would have accepted translations of, "I was reading it," "I am reading it," or, "I will be reading it."