Verified answer

For いAdjectives use the plain form with the い and add のだ

For なAdjectives use keep the な and add のだ

For nouns and verbs just add のだ to the plain form

This is just another way of giving a reason in Japanese. Its like saying because of this.

EG Pretend someone asked you why you shop at the supermarket your answer could be:　

スーパは便利なのだ

スーパはべんりなのだ(su-pa wa benrina noda) －Because the store is convinient.

のだ (のです) and んだ (んです) are used at the end of a sentence for emphasis. They are also used to ask questions.

* <formal> のです, <informal> んです、のだ、んだ

- "I am reading a beginners level japanese book,

<masu form> Watashi wa aru shoshinsha level no Nihongo no hon wo よんでいます (yon de imasu),

<のだ form> Watashi wa aru shoshinsha level no Nihongo no hon wo よんでいるのだ (yonde iru noda),

- "and I need to know what this form means and how it works."

<masu form> soshite watashi wa kono form ga nani wo imi suru noka to dono you ni hataraku no ka wo shiru hitsuyou ga あります (ari masu).

<のだ/んです form> soshite watashi wa kono form ga nani wo imi suru noka to dono you ni hataraku no ka wo shiru hitsuyou ga あるのだ (aru noda)/あるんです (arun desu).

- "How does the のだform work for verbs?

<desu form> のだ form wa doushi ni dono you ni はたらくのですか (hataraku no desu ka)?

<のだ/んだ form> のだ form wa doushi ni dono you ni はたらくのだ (hataraku noda)/はたらくんだ (hatarakun da)?

- "and why?"

<desu form> sohite なぜですか (naze desu ka)/なぜなのですか (naze nano dezu ka)?

<んです form> shosite なぜなんですか (naze nan desu ka)?

* なぜんです, なぜんだ, and なぜのだ are ungrammatical, they shold be なぜなんです, なぜなんだ, and なぜなのだ respectively