When I first decided to build a PC this analogy helped me so much I still use it to explain to the PC illiterate. (Not a perfect explanation)

Cabinets/Refrigerator = Harddrives

This is where you keep your food while it waits to be use.

A hard drive (HDD) is where your games, programs, Operating system (windows) are stored.

Countertops = Ram

More counter space means you can prepare more/larger foods at the same time effectively by allowing you to pull the foods from the cupboards and set them on the counter in preparation of needing them.

Ram allows your PC to access stored information quickly by collecting the needed information.

Note: while not a perfect explanation this is to assist the illiterate person to understand the basics.

Floor space/Staff = CPU

With a larger kitchen you can have more staff working on the meal, thus generally meaning the meal gets prepared quicker.

The CPU allows functions to be performed quickly and effectively. The larger a CPU the more tasks can be handled and the quicker it is done.

Note: Again a generalization to simplify.

Edit: Honestly, if this can help one person to understand even just a little then I'm happy.