CPU: Central Processing Unit:  The CPU is the part of the computer that does the actual "computing."  Often it's just the size of a book of matches.  Using Walmart as an example, a cashier would be like a CPU "Processing a line of commands."  In the kitchen example, it would be the cook.  

CPU Speed: The processing that a CPU does is like quickly turning light switches on and off, or maybe the swinging of pendulum clock.  Every switch or swing would be a tick of activity, taking a step in running your programs.  The faster the CPU speed ticks (usually measured in Gigahertz) the faster the computer processes its line of commands.  Also, the faster the speed, the hotter the CPU gets which is why computers need fans.  If they get too hot they fail...just like heat stroke.  One challenge in designing laptops is how to keep the processor cool when there is little air space or airflow for a fan to cool it down.  
Single Core Processor (CPU):  One Cashier processing one line of commands.

Hyper-Threaded Processor (CPU):
 Hyper-threading is a technology that (according to Intel) uses previously unused resources on a processor to assist with multi-tasking.  The assistance generally equates to 30-40% improvement in performance.   So a Hyper-Threaded Single Core processor processes one line of commands at full speed and a second line of commands at a reduced speed but still gets more done in the same time.  In the Walmart example, it is like the cashier has three arms. The cashier can run the register and move stuff down the belt and bag all at the same time. 

Dual Core Processor (CPU): Two cashiers, each running their own checkout...twice as many people (programs) get processed.

Core i3, i5, i7 (CPU):  Hyper -threaded dual core processors.  Two cashiers, both have three arms. Sometimes they also have Turbo Boost. Turbo Boost can sense a large task and the summon up more speed.  In a car engine it would be like the four barrels kicking in. At Walmart, the two cashiers see their lines backing up and run faster to process their line faster than usual to handle the large line.  Some i5 and i7 are Quad Cores...usually denoted by a "Q" in the model number.

Quad Core (CPU):  Four cashiers at Walmart.  Or maybe four straws in your glass of milk passing four times the milk (data) with essentially the same effort...doing four things at once.

RAM: Random Access Memory:   RAM Modules or sticks are the part of the computer where programs are actually running.  In a kitchen for example, RAM would be the counter space.  If you want to make a sandwich (run just one program) then you don't need much counter space (RAM).  But if you wanted to make Thanksgiving dinner (run many programs, browsers, pages all at once) then you's need more counter space...(RAM).    

Hard Drive/Hard Disk Drive:   The hard drive, is the part of the computer where Information, Programs, Windows, Documents, Pictures, etc  are stored. In the Kitchen would be the refrigerator   Hard drives can fail.  It's one of the few moving parts of a computer.  In a laptop it is about the size of a deck of cards.  In a desktop, it's about the size of a VCR Tape or church hymnal.  Some things that can cause failure include the jarring movement of dropping a computer, or power surges, static shocks, and sometimes viruses.