Learn Farsi: یک سوال از معلم بپرس.

It comes from the verb پرسیدن (porsidan), which means "to ask." To make a singular command (telling one person to do something), we take the present stem, which is پرس (pors), and add the command prefix بـ (be-) to the beginning.

Why do we use از (az) before معلم (mo'allem)? Doesn't that mean "from the teacher"?

Yes, از (az) means "from." In English, you ask someone a question directly, but in Farsi, you ask a question from someone. That's why the sentence literally translates to "Ask a question from the teacher."

Where is the word for "the" in "the teacher"?

Farsi doesn't have a direct word for "the." Because معلم (mo'allem) doesn't have the word یک (yek - a/one) in front of it like سوال (so'al - question) does, we understand from the context that it means a specific teacher.

Why is the command word بپرس (bepors) at the very end of the sentence?

Just like in regular statements, verbs in Farsi almost always go at the end of the sentence. Even though English puts the command "Ask" at the very beginning, Farsi keeps بپرس (bepors) at the end.