In this lesson, I will introduce you the expression using んです, which is used to explain things.

んです follows plain form of verbs, adjectives, and nouns.

In response to the utterance, "You look tanned!"

ハワイ　に　いったんです。

I went to Hawaii.

*いった is past tense plain forms of いく, go

*んです explains the reason why you look tanned.

どうして　きのう　パーティ　に　こなかったんです　か。

Why didn't you come to the party yesterday?

きのう　は　おきゃくさん　と　うちあわせ　が　あったんです。

I had a meeting with a customer yesterday.

If you were Chinese, and someone talk to you in Japanese, you can say,

ちゅうごくじんなんです。

I am Chinese.

In response to your neighbor's utterance, "Your dog runs fast!",

げんきなんです。

He is healthy.

どうしたんですか。

What happened?

あたま　が　いたいんです。

I have a headache.

References:

Introduction to Plain Forms

https://anchor.fm/yuya-sato/episodes/Introduction-to-Plain-Forms-enp0g3

Plain Forms in Past Tense

https://anchor.fm/yuya-sato/episodes/Plain-Forms-in-Past-Tense-eoe8fp

Describing a Person's Feature

https://anchor.fm/yuya-sato/episodes/Describing-a-Persons-Feature-ennovs

Adjectives

https://anchor.fm/yuya-sato/episodes/Adjectives-en9o8v

Instagram:

https://www.instagram.com/yuyaman1986