what is the main function of chapter 23?

This is a bit mutch for this short answer forum but hopefully this helps:

Nurse Ratched has reasserted her control over the institution in Chapter Twenty-Three, again a mother or a warden who dominates the men. She speaks to them in utterly condescending terms, even referring to them as “boys” and treating them as children who cannot accept any sense of responsibility. Having treated these men with such great disrespect and taking away something of value to McMurphy, she triggers his anger. He responds with impudence. When he breaks the glass, this is the first physically aggressive action he takes against Nurse Ratched. This brings the confrontation between the two characters back to the fore, for McMurphy is aggressively acting out on behalf of the privileges of the patients. He is taking a risk in that the act will mean a longer stay in the institution, but at this moment his anger or rebellion is stronger than such a fear.