Learn Hardcore Russian: Читай книгу, пока тебе интересно.

читай is the 2nd person singular imperative of читать (to read). It’s in the imperfective aspect, which emphasizes an ongoing or repeated action rather than a single completed event.

Why is the verb in the imperfective aspect here, not perfective?

The imperfective aspect is used because the instruction is about reading as long as it continues to be interesting. A perfective form (e.g. прочитай) would imply completing the whole reading once, regardless of interest.

Why is книгу in the accusative case?

книгу is the direct object of читай. In Russian, the thing you read must be in the accusative case.

What does пока mean in this sentence?

Here пока means “while” or “as long as.” It introduces a subordinate clause indicating the time during which you should keep reading.

Why is тебе in the dative case in пока тебе интересно?

The adjective/adverb интересно forms an impersonal construction: “it is interesting to you.” In such constructions, the experiencer (you) goes into the dative case, hence тебе.