It seems that in no language, concerning the use of pronouns, a distinction is made between a noun and an idea. That's not the case in English nor in Italian. (At least in the case of the interrogative pronouns. In the case of the relative pronouns, there is a difference.)
a) What are you eating?
b) What did you do yesterday?
In case a) the response is a simple noun (apple, bar of chocolate, yoghurt). In the case of b) the response is an idea, an amount of words (I went swimming; I cleaned the appartement etc.). Later we will see that in the case of relative pronouns it is necessary to understand the difference between a simple noun and an idea, but the relative pronouns are an exception. Decide whether in the following sentences "che cosa", "cosa" refers to a noun or to an idea.