Just plug your USB Flash Drive into the USB port of your computer or other USB-equipped device. If the flash drive has a light (LED), it will flash to indicate it's operational.
Your computer may recognise a new drive has been detected, and prompt you to open the drive (or run files already on the drive). Choose the option to 'open' or 'explore' the new drive.
If you are running Microsoft Windows as an operating system, you can also see the new drive by clicking 'My Computer' on the 'Start' menu which lists all your computer's drives, including the flash drive. Double click the flash drive to open it.
Drag the files you want to copy to the flash drive into the folder that appears on your screen. Your files are now transferred to your USB Flash Drive (normally instantly but it can take a little longer if the files are big).
You can unplug your flash drive at any time, as long as files are not being read from or written to the flash drive. Ensure the LED is not flashing if your device has one.
To transfer the items on your USB Flash Drive onto another computer, explore the files on the flash drive as above, and the drag them to a location on the new computer.