Learn Polish: Nauczyciel pytał, ale nic nie wiedziałem. - The teacher asked, but I knew nothing.

In the Polish past tense, the ending tells you who is doing the action. The -ł in pytał is the 3rd-person ending for a masculine subject, used here for "he" (the teacher). The -łem in wiedziałem is the 1st-person ending, meaning "I" (a man speaking).

Does wiedziałem tell us if the speaker is a man or a woman?

Yes! The -łem ending is specifically used by a male speaker. If a woman were saying this sentence, she would use the feminine ending -łam and say wiedziałam.

Why does it say nic nie? Doesn't that mean "nothing didn't"?

In Polish, double negation is completely normal and grammatically required. When you use a negative word like nic (nothing), you must also put nie (not) before the verb. So nic nie wiedziałem literally translates as "I didn't know nothing", which is just how you say "I didn't know anything" in Polish.

Why isn't the word for "I" (ja) in the second half of the sentence?