kupić

In a sentence

• Chcę kupić książkę w tej księgarni.

  I want to buy a book at this bookstore.

  In this sentence, 'kupić' means 'to buy' and is used in its infinitive form to express the intention of purchasing an item.

• Kupiłam wczoraj świeże warzywa na targu.

  I bought fresh vegetables at the market yesterday.

  In this sentence, 'kupiłam' is the past tense form of 'kupić' (in the first person singular, feminine) indicating a completed action of buying something in the past.

• Muszę kupić mleko przed powrotem do domu.

  I need to buy milk before returning home.

  Here, 'kupić' is used in its infinitive form as part of the phrase indicating necessity (with 'muszę', I need) of performing the action of buying in the future.