In front of a noun:
At the end of a sentence:
Negative:
Past:
Past negative:
Joining and adverb:
A な-adjective is a describing word that needs な between it and the noun it describes: しずか静かなまち町 is a quiet town. At the end of a sentence there is no な, and です follows the word directly.
An い-adjective goes straight onto its noun; a な-adjective needs な. An い on the end does not settle which kind it is, so learn the kind with the word. Three common な-adjectives end in the sound い and look like い-adjectives: きれい (pretty, clean), きらい嫌い (disliked) and ゆうめい有名 (famous).
The い-adjective endings do not go on a な-adjective, and な does not go on an い-adjective.
Leaving な out in front of a noun, and keeping it at the end of a sentence, are both wrong.
A な-adjective itself never changes. The negative and the past are made the way they are for a noun, by changing です.
じゃ is では said quickly. The じゃ forms are what you hear in conversation; the では forms are more formal.
These go beyond the polite forms.
In casual speech です becomes だ, and the other forms are じゃない, だった and じゃなかった.
Some な-adjectives stand where English has a verb or a phrase: すき好き (liked), きらい嫌い (disliked), じょうず上手 (good at), へた下手 (bad at). The thing liked or done well takes が.
To say "and" after a な-adjective, add で.
With に a な-adjective describes how something is done.