How can I copy an icon from a .icns file onto another folder or file?

Using Finder go to the folder where the icns file is located. Open this icns file using Preview. Once the file is open click on select all in the edit menu item. Once you've selected all, open a file in Pages and paste the image in the new or old file. This file now contains the image.

I ended up opening doing this:

1. Open the icns file in GraphicConverter.
2. Select Edit → Select All (or press Command-A) to select the entire image.
3. Select Edit → Copy → Copy (or press Command-C) to copy the image.
4. In the Finder, select Go → Computer (or press Command-Shift-C) to navigate to Computer.
5. Click on the hard drive you want to copy the icon to.
6. Select File → Get Info (or press Command-I) to open the info window.
7. Click on the small “proxy icon” to the left of the drive’s name.
8. Select Edit → Paste (or press Command-V) to replace the drive’s current icon with the copied image. You may be prompted for an administrator password if you’re changing a drive icon.

The same procedure works on ordinary files and folders, too, not just drives.