The two kinds of adjective
A-い / A-な
Japanese has -い adjectives (大きい, 高い) and -な adjectives (きれい[な], 有名[な]). They behave differently when modifying nouns and when conjugating, so it pays to memorise each adjective together with its type.
Examples
富士山は 高いです。
Mount Fuji is tall.
桜はきれいです。
Cherry blossoms are beautiful.