"It is not ours."
Translation:Es ist nicht unsere.
nicht is an adverb which negates the verb of the sentence. In this case the verb is
sein, conjugated in third person singular:
er/sie/es ist. Here is how to say "No" in German: http://german.about.com/od/grammar/a/German-Negation.htm
Not an expert, but it seems that nicht usually (always?) comes directly after the verb 'sein' (ich/bist/ist/sind etc.). With other verbs nicht comes at the end.
For example, 'Es ist nicht unser Hund' vs 'Es sieht unseren Hund nicht'
'It isn't our dog' and 'it doesn't see our dog' respectively.
But I may be corrected.
It really depends on the type of verb (separable or compound) and the type of sentence (declarative or not).
Read more about the position of nicht: http://german.about.com/od/grammar/a/The-Position-Of-Nicht.htm
The sentence is about something which is not ours. Personal pronoun "es" stands for a noun (say: pro-noun) while "it" does not specify its gender. So the unknown subject might be male, female or neuter: Here an example with a typewriter (German: die Schreibmaschine) which is not ours: Was ist das? Eine Schreibmaschine. Ist das eure Schreibmaschine? Es ist nicht unsere [Schreibmaschine].