If you intend to reformat and reinstall your system, you can put
your files in a separate partition that you have created. (And that
is if you have created).
Usually, Windows is installed on C drive. If you have more than C
drive, just move your important files to that partition will do.
And don't format the partition, otherwise, your files will be
gone.
You can also use external media storage like CDs, DVDs and USB
HDD.
For CDs and DVDs, check your burning program for more details. It's
usually just a drag and drop or adding files to it. For USB HDD,
it's just drag and drop.
Another way would be to use imaging software like Acronis True
Image or Norton Ghost. That's if you have them and know how to use
them.
Acronis
True Image
Backing
up using Norton Ghost