Proper Adjectives are derived from proper nouns.
eg : a. Chinese soldiers fought bravely.
b.We are studying the English language.
In ( a ) the word " Chinese " is a proper adjective because it is derived from the proper noun " China "
In ( b ) the word " English " is a proper adjective because it is derived from the proper noun " England ".
Note -- Every proper adjective should begin with a capital letter.