Questions & Answers about Wczoraj byłam w kinie z moim bratem.
How do we know the speaker of this sentence is female?
The verb byłam (I was) has the feminine ending -am. In the Polish past tense, verbs change depending on the gender of the speaker. If a man were saying this sentence, he would use the masculine form byłem.
Where is the word for "I" in this sentence?
In Polish, subject pronouns like ja (I) are usually left out because the verb ending already tells you who is doing the action. The -am at the end of byłam clearly means "I (female) was". You would only add ja if you really wanted to emphasize it.
Why is it w kinie instead of w kino?
The preposition w (in) is used here to describe a location, which requires the noun to be in the Locative case. To form this case, the neuter noun kino (cinema) drops its final -o and takes the ending -ie, becoming kinie.
Why does it say z moim bratem and not z mój brat?
The preposition z meaning "with" requires the words that follow it to be in the Instrumental case. The basic phrase mój brat (my brother) changes its endings to match this rule, becoming moim bratem.