STRUCTURE

NOUN CLAUSES BEGINNING WITH THAT

Statement         

•  He is a good actor
• The world is round

Noun Clause      

1. I think that he is a good actor
2. I think he is a good actor
3. We know (that) the world is round

In (1) : that he is a good actor is a noun clause. It is used as the object of the verb think.
The word that, when it introduces a noun clause, has no meaning in itself. It simply marks the beginning of the clause. Frequently it is omitted , as in (2), especially in speaking (if used in speaking, it is unstressed.)

Statement

• She dosen't understand spoken English
• The world is round

Noun Clause

1. That she dosen't understand spoken English is obvious
2. It obvious (that) she dosen't understand spoken English
3. That the workd is round is a fact
4. It is a fact that the world is round

In (1) : The noun clause (That she dosen't understanding spoken English) is the subject of the sentence. The word that is not omitted when it introduces a noun clause used as the subject of a sentence, as in (1) and (3).
More commonly, the word it funtions as the subject and the noun clause is placed at the end of the sentence, as in (2) and (4).