Which is correct:
"Darkness is needed to know the importance of light"
"Darkness be needed to know the importance of light"
I don't know too much English so if anything wrong here please explain :)
"Darkness is..." is the better option.
"Darkness" is a singular noun, so usually takes the third-person singular conjugation of a verb. The third-person singular of the verb "to be" is "is."
If you used "be" instead, everyone would know what you meant, but in that situation it would sound unnatural.
I think in modern English you would only use ‘be’ to indicate something that is going to happen in the future. For example. Today there is one ship in the harbour. Tomorrow, there will be four ships in the harbour.
Darkness is needed to know the importance of light. Tomorrow, darkness will be needed to know the importance of light.
“Darkness be needed…” is not wrong, but it does sound awkward or old fashioned. IF you are telling a story or writing poetry you might speak that way on purpose.