Constructing a sentence having a noun clause is very simple. One of the easiest ways is to begin a sentence like this:

He said that…

Whatever clause you put after ‘that’ will automatically become a noun clause.

He said that he would come.
He said that he was interested in the offer.
He said that he was busy.
He said that he had received the letter.

Instead of the verb ‘said’, you can use any of the following verbs.

Know, believe, think, realize

I think that she is very intelligent.
I realized that my decision was wrong.

Feel, hope, understand, wish

I felt that it was a good offer.
I understand that I can be wrong.

See, notice, find, discover, note

I noticed that something was amiss.
I discovered that he was cheating on me.

Hear, listen

I heard that there was an explosion.

Say, tell, ask, request, order

He told me that he would come.
He ordered that we should go at once.

Explain, suggest, reply, inform

Mother suggested that I should consult a doctor.
He informed us that there was a problem.