Learn Polish: Kiedy lekarz każe mi odpoczywać, odpoczywam. - When the doctor tells me to rest, I rest.

The verb kazać (to order / to tell someone to do something) requires the Dative case for the person receiving the order. mi is the short Dative form of ja (I). We use the short form mi instead of the long form mnie because it is not at the beginning of the sentence and we aren't putting special emphasis on "me".

The verb każe translates to "tells" here. What is the dictionary form?

The infinitive is kazać. Even though it directly translates as "to order" or "to command", it is very commonly used in Polish just like the English phrase "to tell someone to do something". Be careful not to confuse it with karać (to punish).

Could I put mi at the end of the clause, like Kiedy lekarz każe odpoczywać mi?

It is best to avoid that. mi is a short, unstressed pronoun. In Polish, short pronouns like to tuck themselves into the middle of a phrase and sound unnatural at the very end of a sentence or clause. Placing it right after the main verb każe is the most natural word order.

Why use the imperfective verb odpoczywać instead of the perfective odpocząć?