Insert the flash drive into the USB port on the computer. Review Portable Storage lesson, if necessary.
Open File Explorer.
Find the file you want to save to the flash drive.
Drag it from its current location to the flash drive in the menu on the left.
(Note: I have renamed my flash drive to "Memory Stick," yours will not have this name.)
Dragging the file to the flash drive will not remove the file from its original location, it will only make a copy.