だったform （How to use it)

 In Japanese, the "datta" form is a past tense form used to describe states or actions that occurred in the past. It's often translated as "was" or "were" in English.

How to form "datta"
Identify the dictionary form of the verb or adjective.

Breaking down "きれいだった" (kirei datta)
きれい (kirei): This is an adjective meaning "beautiful" or "clean."
だった (datta): This is the past tense form of the copula "だ" (da), which is used to connect a subject with a predicate.
When to use "datta"

Describing past states:
Example: 昨日は暑かった。(Kinō wa atsukatta.) - Yesterday was hot.
Describing past actions:
Example: 私は昨日映画を見ました。(Watashi wa kinō eiga o mimashita.) - I watched a movie yesterday.
Expressing past experiences:
Example: 子供の頃は、よく公園で遊んだ。(Kodomo no koro wa, yoku kōen de asonda.) - When I was a child, I often played in the park.
"Datta" vs. "Deshita"

"Datta" is used with verbs and adjectives.
"Deshita" is used with nouns and is a more polite form of "datta".
Examples

With verbs:
私は昨日、本を読みました。(Watashi wa kinō, hon o yomimashita.) - I read a book yesterday.
With adjectives:
海はきれいでした。(Umi wa kirei deshita.) - The sea was beautiful.
With nouns:
彼は医者でした。(Kare wa isha deshita.) - He was a doctor.
In summary:

The "datta" form is a versatile tool in Japanese grammar. It allows you to describe past events, states, and identities. By understanding how to form and use "datta," you can express yourself more accurately and effectively in Japanese.