Types of Adjectives

Please read nouns first.
Japanese has two main types of adjectives い(“e”) adjectives and な(na) adjectives. Both types of adjectives modify nouns.
They may be placed either before a noun, or at the end of a sentence:

• AはAdjective — A is adjective.
• Adjective AはB — Some kind of A is B.
  
  

い Adjectives

い adjectives are sometimes called “true” adjectives. Almost all い ending adjectives are い adjectives. い adjectives can modify nouns as they are. You may useです, but not だ, after an い adjective. 

The reason to use です and not だ after an い adjective is that です makes it more polite.
Using だ doesn’t change the meaning vs not using だ, so there is no reason to use だ。

If an adjective ends with い only ones that end with an えい sound may be な adjectives. 

Common い Adjectives

• たのしい (tanoshii) – Fun
• おもしろい (omoshiroi) – interesting/funny
• うれしい (ureshii) – happy
• かわいい (kawaii) – cute
• こわい (kowai) – scary

Examples

• たのしいひと (tanoshii hito) – Fun person
• がっこうは　たのしいです (gakkou ha tanoshii) – School is fun. 
• かれの　いもうとは　かわいい (kare no imouto ha kawaii) – His (younger) sister is cute. 
• とらは　こわい (tora ha kowai) – Tigers are scary. 

な(na) Adjectives

The other main category of adjectives is な adjectives. These adjectives modify nouns by using な.
Most of them are/can function as nouns in their own right, and in most cases behave exactly like nouns, except for using な instead of の. 
They must use だ・です (like nouns) at the end of a sentence. I have been omitting this with nouns so far for simplicity.  

The reason you need a だ or です at the end of a sentence with な adjectives is in part because of the “noun” aspect of な adjectives, but also because it originated from a kind of だ。
Source: (断定の助動詞「だ」の活用形)

For adjective conjugations, please see the Adjective Conjugations page.

Common な Adjectives

• きれいな (kirei na) – pretty
• にんきな (ninki na) – popular
• べんりな (benri na) – convenient
• ひまな (hima na) – free/bored/nothing to do
• おおきな (ooki na) – big

Examples

• きれいな　ひとだ (kirei na hito) – Pretty person
• かれは　ひまだ (kare ha hima da) – He has nothing to do/bored. 
• おおきな　さかなだ (ookina sakana) – Big fish. 
• このみせは　べんりだ