kolegą

In a sentence

• Odwiedziłem wczoraj mojego kolegę.

  I visited my friend yesterday.

  Here, 'kolegą' is used in the instrumental case connected with 'mojego', indicating an action involving a colleague.

• Piotr jest moim kolegą z pracy.

  Piotr is my colleague from work.

  Here, 'kolegą' is used to describe a relationship using the instrumental case.

• Poszedłem na spacer z kolegą.

  I went for a walk with a friend.

  Here, 'kolegą' is used in the instrumental case to indicate companionship during the action of walking.