koc

In a sentence

• Przykryłem się kocem, bo było mi zimno.

  I covered myself with a blanket because I was cold.

  Here, 'kocem' is the instrumental case form of 'koc', used to describe the item being used to perform an action, in this case, to cover oneself.

• Położyłem koc na kanapie.

  I put the blanket on the couch.

  In this sentence, 'koc' is in its nominative form as the subject of the action of placing.

• Nie mogę znaleźć mojego ulubionego koca.

  I cannot find my favorite blanket.

  Here, 'koca' is the genitive case form of 'koc', signaling possession or lack thereof for the noun.