Na adjectives can't be declined like i adjectives can. So for instance, "omoshiroi" is an i adjective that means "interesting" and "omoshirokunai" means "not interesting". "Kirei" is a na adjective that means both "pretty" and "clean". To say "not pretty", you have to place the simple negative form of the copula after it. So "Kirei ja nai" and "kirei de wa nai" mean "not pretty". When you use a na adjective before a noun, the particle "na" has to come between it and the noun, so "kirei na hana" means "pretty flowers". An i adjective just comed before a noun as is. So "omoshiroi eiga" means "interesting movies". I adjectives have past tense declinations so "omoshirokatta" means "were interesting" and "omoshirokunakatta" means "weren't interesting". Na adjectives have to be followed by the copula in the past tense, so "kirei datta" means "were pretty" and "kirei ja nakatta" means "weren't pretty".

Besicly it classfied dictionary from end up I or Na In conjugation is different in I and Na Adjective. In learning grammar need to identify those adjective . ex Utsukushii Hana (Beautiful flower) I adjective + noun /Kinarina Hana (beautiful flower) Na Adjective + noun But when verb comes Ex Utsukshiku Naru (become beautiful ) I adjective end change I into shiku + verb kineri ni naru (become beautiful) Na adjective na cross out + Ni (partical) + verb Na Adjective therfore when make sentence grammartical conjugation forming is differece in two adjectives You learn more you understand more about conjugation when you understand you can understand more about 2 adjective Other specifacation is Na adjective is very near kin of Noun.