This is how we add something descriptive to nouns.
Verbs
To modify a noun with a verb we need to use the standard form of the verb before the noun which we want to modify.
食べる 時間。
Time to eat.
見た 映画。
Film I saw.
送る 手紙。
Letter to send.
飲まなかった コーヒー。
Coffee I did not drink.
買わない 傘。
Umbrella I will not buy.
The same logic applies to the auxiliary verb. In the above sentences the subject is assumed to be the speaker because we do not have enough information to know otherwise.
先生じゃない 人。
Person who is not a teacher.
学生だった ころ。
Time when I was a student.
学生じゃなかった 美紀子。
Mikiko who was not a student.
For the affirmative auxiliary verb we need a third form of the auxiliary verb which will be introduced later.
学生である 人。
Person who is a student.
Adjectives
Similar to English, to modify a noun with an adjective in Japanese we simply place the adjective before the noun.
The car.
The expensive car.
I-Adjectives
I-adjectives are simple. All we need do is place them before the noun we want to modify.
おいしい 料理。
Delicious food.
安い 財布。
Cheap wallet.
We can only modify the noun with the standard form of the adjective. In Japanese, whether the sentence is standard or polite is determined by the form of the final verb.
やさしいです 先生。(✘)
やさしい 先生。(✔)
Kind teacher.
What about negative sentences? Well, we can either modify the adjective or modify the auxiliary verb which give rise to the same meaning but using slightly different logic—as is the case in English.
面白くありません 映画。(✘)
面白くない 映画。(✔)
Uninteresting film.
彼は やさしくない 先生です。
He is an unkind teacher.
彼は やさしい 先生ではありません。
He is not a kind teacher.
A similar logic applies to past and past negative sentences; however, here it is almost always more natural to modify the auxiliary verb.
彼は やさしかった 先生です。(△)
He is a teacher that was kind.
彼は やさしい 先生でした。(OK)
He was a kind teacher.
Na-Adjectives
I-adjectives are so called because they end with い. Na-adjectives, on the other hand, do not end with な. This is a syllable we need to add to the adjective when modifying nouns.
【na-adjective】＋ な ＋【noun】
彼女は きれいな 女性です。
She is a beautiful lady.
ここは 便利な 場所です。
This is a convenient place.
これは 有名な 映画です。
This is a famous film.
Note also that the auxiliary verb is omitted. In other words, the following is incorrect:
ここは 便利だな 場所です。(✘)
This is a convenient place.
What if we want to form negative, past, or past negative tense expressions? Here we include the auxiliary verb and exclude the な syllable.
彼女は まじめだった 学生です。
She is a student that was serious.
But, as before, modifying the auxiliary verb is far more natural in the vast majority of cases.