multiple drives and NAS?

I'm a new CCleaner user.

I can't see where to choose which drives ti include in the cleaning process.

I followed instructions and went to setting and browse for which drives and clicked add/OK and was told: "for system safety reasons you cannot select this specific location"

I tried to add a folder within the drive and I was given the warning "warning - this folder will be emptied of all files upon cleaning".

Well I don't want to empty these folders I just want to clean them. And I have C, D and an NAS drive. How do I include them? Am I just misunderstanding how CCleaner works? Is it automatically including the D drive and NAS? If not, how can I tell where I want free space wiped or duplicates found etc?

Any help would be greatly appreciated.