This is elementary stuff:
A computer will only run one OS at a time.
There is at least one huge desktop case that can house two separate motherboards if you want to run two OSes at the same time and switch between.
Also KVM switches for two separate machines to use the same monitor/mouse/keyboard.
If you want to write to Windows NTFS files from within OSX the easiest way is to buy a program that does that, e.g Paragon (I use it) for NTFS--OSX can read but not write to NTFS formatted drives. Similarly if you want to access OSX journalled drives from within Windows . . .
If you want to run Windows programs, not games, from within OSX emulators sort of work, like, ugh, Parallels--that requires a complete install of the Windows OS into the virtual machine. The use of Parallels will burn into most people's minds the meaning of the word "kludge" and gift the experience of low level ransomware from the vendor (when you upgrade to the latest and greatest OSX you have to pay for the corresponding Parallels upgrade that doesn't work any better than ones you already paid for).