Thank you Aleksandra. I'll check the link also

In general 'narzędnik' answers the question with whom / with what?

For example:
1. Z kim idziesz do kina?
Who are you going to the cinema with?
Idę z Anią.
I am going (there) with Ania.
Z kim? Z Anią.

2. Z czym pijesz kawę?
How do you like your coffee? Literally: What do you drink coffee with?
(Piję kawę) z mlekiem / z cukrem.
(I drink coffee) with milk / with sugar.
Z czym? Z mlekiem / z cukrem.

More information can be found here:
http://www.polskinawynos.com/?p=1435