Looking at the images and the boxes, it goes like this;
To add external functionality of external backup, you would probably have something removable from the computer accessable. This means that the Optical Drive would add functionality of external backup, and the first tile goes there.
A processor is what does the general computations inside a laptop/desktop computer and processes information as the name implies. Upgrading the processor makes it go faster. The second tile would go to the processor.
The third one need no further explanation and would go to the Hard Drive, but just keep in mind that the Hard Drive stores all the information on your computer (i.e. Applications, Photos, etc.).
Hope this helps!
