んです（N５)

When you have a fact that you want to emphasize and let them know, it may be better to use "んです".

It is also used to make sure the situation from the information obtained by seeing and hearing.

Japanese use this with our sense, so you can use it without worrying too much.         

How to use			examples	Translation
Verb	Present/Past/Negative Short form	＋んだ/んです	かいたいんですが、おかね　が　ないんです。	I want to buy it, but I have no money.
いadj	Present/Past/Negative Short form		きょうは　あついんです	It's hot today
なadj	Present Short form + な		コーヒ が すきなんです	I like coffee
	Negative Short form		コーヒ が すきじゃないんです	I do not like coffee
	Past Short form		まえはコーヒーがすきだったんです	I used to like coffee
Noun	Present Short form + な		あした　は　はれなんです	It's sunny tomorrow
	Negative Short form		あした　は　はれじゃないんです	It's not sunny tomorrow
	Past Short form		きのう　は　はれだったんです	It was sunny yesterday

Exercises

Genki1

Genki 1 Work book