"Jabłko jest dobre."

Translation: The apple is good.

[Matthew_Phelps]

So is "dobre" the singular, neuter, nominative form of "good" ?

[Latcarf]

Yes

[Svayone]

K, I'm russian, and "dobre" on russian sounds like "kind", and just imagine: kind apple

[Jellei]

"kind" can be also a translation of Polish "dobry"... where it makes sense, of course ;)

[A477]

Shouldnt it be Jablko jest dobrym? since after jestem, jestesz etc its instrumental case?

[immery]

No. In the "noun is adjective" type of sentence, you use adjective in nominative, and you can't use "to"

[Leona783456]

What's the difference between dobrze and dobre?

[alik1989]

Dobrze is the adverb, dobre is the neuter singular adjective.

Most adverbs are formed by adding -ie to the stem, and this is also the case here.
You just have to apply the phonological rule r + i -> rz.

[KlaudiaJucha]

Jabułko ???

[Jellei]

What's the question? That's not how it's written.