How do you copy document files from an external HDD to the HDD inside the computer?

This process differs depending on your Operating System, but in most Windows computers, this process can be accomplished by first connecting your external hard drive, then clicking "Start". You can then click "My Computer" and find the external hard drive in the drives listed there. Then, double-click on the external hard drive's icon, and find the files you want to transfer. Right click on them, and select copy. Next, open the directory on your computer that you want to transfer the files to. Then, right-click and hit paste.