Learn Italian: Tutto era diverso, qui non c'era niente. - Everything was different, there was nothing here.

Era is the imperfetto (imperfect) tense of essere (to be). We use the imperfetto to describe how things used to be, to set the scene, or to talk about ongoing states in the past. Because we are describing an ongoing past state ("Everything was different"), era is the correct choice over the passato prossimo (è stato), which is used for completed, isolated events.

Is tutto treated as singular or plural here?

In this sentence, tutto means "everything" and acts as a singular subject. That is why it takes the singular verb era and the singular adjective diverso. If you wanted to say "all the things", you would use the plural tutte le cose, which would then take the plural verb erano.

How is c'era formed?

Just like the present tense c'è (there is) combines ci (there) + è (is), the past tense c'era combines ci + era (was). The i in ci is dropped because era starts with a vowel, giving us c'era (there was).

Why is there a non in the second half if the sentence already has niente (nothing)?