How to copy or save a file to a USB device such as a Flash drive.
The two basic ways are:
1) Plug in the drive to a USB port.
2) If the document is open in whatever program you used to create it such as "Word", you can simply "Save" that document to the USB device using the "Save As" command. This changes the default save location to the USB device.
But remember that at this point, the only copy is going to be on the USB device, not on your computer. You may want to save it to the default folder such as the My Documents folder first and then to the USB.

A better way is to first save the file to the default location and then open Windows Explorer, find the document on your hard drive, right-click it, and choose "Send To", the USB device. Many people do not know where their documents get saved.
Find this out before saving the file. Usually they are in Documents or My Documents folder by default. under the User's name.