I still didn't get the mac yet so don't know about that specifically. I guess OS X Yosemite comes on the 2015 MacBook Pro 13" Inch 256GBIt really depends on the model of mac you have, the version of Mac OS X you are running, and the processor type(32 or 64 bit)
If you want to install Windows on your Mac natively, you would use Boot Camp 5.1, on a modern, up-to-date Mac. It has support for Windows 7, 8, and 8.1.Windows 8.1 64-bit. The windows you install on day today PC's or Laptops(which are not Macs).