In Japanese, some nouns can be used in an adjectival way by placing them prior to what they should modify, and appending な.
Nouns that cannot be used in this way (proper nouns, for example) can instead be used in an adjectival manner through the use of the の particle.1
Example: The bad dog is sleeping
やんちゃないぬがねている
Info
やんちゃ (naughty) is the noun being used in an adjectival manner. な is appended to it in order for it to perform this function and modify the proceeding word いぬ (dog). Together this makes “naughty/bad dog”.
やんちゃないぬ (bad dog) is marked with が, making it the core of the sentence.
ねて (sleeping) is the continuous form of sleep. This tells us more about the main verb of the sentence いる （to be/exist). The core subject exists, and they are sleeping. The bad dog is sleeping.