A noun clause functions as a noun. It can be the subject or object of a verb. A noun clause is a subordinate clause. That means it cannot stand alone.
Study the following sentences.
I don’t believe your story. (Here the noun story is the object of the verb believe.)
I don’t believe what you said. (Here the clause what you said is the object of the verb believe. We have already learned that only nouns can be the subject or object of a verb. A clause that does the work of a noun is therefore a noun clause.)
Now study the pair of sentences given below.
His remarks were objectionable. (Here the noun remarks is the subject of the verb were.)
What he said was objectionable. (Here the clause what he said is the subject of the verb was. A clause that serves as the subject or object of a verb is always a noun clause.)
A noun clause can also be the object of a preposition.
I’m not interested in what she is doing. (Here the noun clause what she is doing is the object of the preposition in.)