How do I transfer data from my hard drive to added external drive

Use AOMEI Partition Assistant to clone your hard drive to extertal drive easily. http://www.disk-partition.com/help/clone-hard-disk.html

Connect your external hard drive to your computer. If the external hard drive is brand new, you will need to format it using the seagate hard drive **** utility. Then highlight all the files you want to copy and right click the mouse, then choose copy. Go to the external hard drive again right click and choose paste. Depending on the number of files  and your computers speed, this may take up to a couple hours.

You can this many different ways. The most straightforward is to go to the drive and select "folder and file options" in the view menu and selct "show hidden files", that way when you copy and paste you will get every single file. The other way is to use a program such as Acronis Tru Image and use the clone option. I am assuming that you want an image of your C:\ drive.