"I am eating with a plastic fork."

Translation: Jem plastikowym widelcem.

[Martynek96]

Ja mialem "Ja jem z plastikowym widelcem" .
Dlaczego to nie było poprawne?

[mihxal]

Because nobody says "z" to express using some tool. "Z" means "with" only in sense "together with" (accompanying). To express using some tool/instrument you should use Instrumental without any preposition like in the sentence above.

[Jakob174045]

One Lingot for you, both for explaining and for answering in English even though the question was in Polish :)

[Martynek96]

Thanks so much!!!

[JHeaven]

Is there a distinction between sztućcem and widelcem for fork?

[Jellei]

"sztućcem" (Instrumental of "sztuciec", usually used in plural: "sztućce") is a piece of cutlery. So it's not a synonym of a fork, as a spoon and a knife also can easily be meant by that word.

[JaniceSchl1]

Why no z?

[Jellei]

If you use something as an 'instrument', there is no "z", just Instrumental without any preposition.

Saying "Jem z plastikowym widelcem" would mean that the plastic fork is sitting next to you, eating as well.