This is the 3rd most frequent Czech word.
že
"Že" is a Czech conjunction meaning "that" or "for," used to introduce subordinate clauses.
Here, 'že' is used as a conjunction to introduce the content of reported speech.
Říkal, že přijde pozdě.
He said that he would come late.
The word 'že' connects the main clause with a subordinate clause expressing certainty.
Jsem si jistý, že to dokážeš.
I'm sure that you can do it.
In this sentence, 'že' introduces a subordinate clause which conveys a thought or idea.