In English, the interrogative adjectives are WHICH or WHAT. They describe which noun.
Which play did you see?
What dress did you buy?
In French, the interrogative adjective is QUEL, but it agrees with gender and number. See the table below:
The form of “QUEL” will modify the noun (change based on gender and number).
-Qu’est-ce que is also a way to say “what”, and you use it in most cases.
-You use QUEL when what is followed directly by a noun, or
Quelle jupe est-ce que tu vas acheter?
-Use a form of QUEL when what is followed by the word “est” or “sont”
Quelles sont tes jupes preferees?
QUEL can also be used as an exclamation “Quelle jolie jupe!” = “What a pretty skirt!”