What is the word 'are' when translated from English to Japanese?

simply, Desu.

eg. who are you? - anata wa dare desu ka?

where are you? - anata wa doko desu ka?

are you ill? - anata wa byouki desu ka?

are they new? - arera wa atarashii desu ka?

ect.

Desu means: Are, Is, and am.