Q: How do I copy folders between an Imac 8.1 hard drive and a flash drive?

Connect the flash drive to the computer. Drag the folder(s) from the hard drive to the flash drive.

Open one folder that contains what you want to copy. Then double-click on the flash drive's Desktop icon to open a second Finder window. Drag from one window to the other.

If both folders appear one on top of the other simply move one or both. You move them by placing the cursor in the window's titlebar area, click the mouse button and hold it down while you drag the window.

Perhaps it would help to read:

Apple - Support - Mac 101

Mac 101- Mac essentials