Learn Polish: Czy gotowałaś wczoraj zupę? - Did you cook soup yesterday?

In the Polish past tense, verbs change depending on the gender of the subject. The ending -łaś is used when saying "you" to a female. If you were asking a male, the verb would be gotowałeś.

How do you build the past tense form gotowałaś from the basic verb?

The dictionary form is gotować (to cook). To make it past tense, you drop the final -ć to get the stem gotowa-, add the past tense marker -ł-, and finally add the personal ending -aś for a feminine "you".

Why is there no word for "you" in this sentence?

Polish usually drops the pronoun ty (you) because the verb ending already gives it away. The -ś at the very end of gotowałaś specifies that "you" are the one doing the action.

Why does the word for soup end in -ę instead of -a here?

The basic dictionary form is zupa. However, because the soup is the direct object of the sentence (the thing being cooked), it takes the accusative case. For feminine nouns ending in -a, that means changing the ending to -ę.