How do I backup my S6 to Windows PC
all you need to know is here http://www.samsung.com/ae/support/smartswitch/ it includes software links for downloads.
How about use a official software of Samsung company? Samsung Kies is supported.
You can transfer or backup files on computer by this software.
If you want to backup data on your S6 to Windows PC, you can ask help from Samsung mobile manager tool. With its help, you can easily transfer, backup data like app, contacts, sms, music, photos, videos, books, call logs on S6 to pc.