[chryuop]

Just to add a little bit more to his answer. のです/んです can be seen as the English verb "happen" or "you know". Like, "you know, we have to buy tickets before enetering the theater" or something of that effect. Many times unfortunately it doesn't have a real translation.

You will learn that some things in Japanese are better to be learnt as per what their role in the phrase is, instead of what they can be translated into. A very good example can be the verb 置く(おく)used as auxiliary after the て form of verbs. I think in many languages it is always translated as a plain future.