wojciechem

In a sentence

• Spotkałem się z Wojciechem wczoraj.

  I met Wojciech yesterday.

  The word 'Wojciechem' is an instrumental case of the name Wojciech, used here to indicate with whom the action of meeting was done.

• Dyskutowałem z Wojciechem na temat języków obcych.

  I discussed with Wojciech about foreign languages.

  Here 'Wojciechem' also appears in instrumental case, used after the preposition 'z' to indicate the person involved in the discussion.

• Pracowałem razem z Wojciechem przez kilka lat.

  I worked together with Wojciech for a few years.

  Again, 'Wojciechem' is in the instrumental case, showing collaboration with the named individual Wojciech in the action of working.