What exactly a Multicore processor does and how does it make a difference?

Whats a multi core processor?

People have often hear that a dual core processor means double power or a quad core processor has 4 times power than a single core processor of same power.So if a processor is lets say 3 ghz quad then it's equivalent to 4x3=12ghz but thats not the case.

So what exactly is a quad core processor? 

Say a 3ghz quad core cpu
It has 4 cpu cores each running at 3ghz
It doesnt mean it has 4 times power!
The more the no of cores the more INDEPENDENT TASKS the processor can handle at that
frequency!
So  a 3ghz quad core processor can handle 4 independent tasks at a time and can give each task a power of 3ghz but thier power cant be shared among the cores.
Lets take a simple example
If 4 friends are given a group project but they all stay very far from each other and cant lend each other a hand so they decide EACH FRIEND will take up  INDEPENDENT TASK of the project as they cant lend each other a hand if one part of the project is dependent on the other.
So this is how a multicore processor works each core can give 3ghz to an independent task so it can handle 4 independent tasks at a time which is diveded among the 4 cores but the cores cant deliver 12ghz(4x power) to a single task
SO A 3 GHZ QUAD CORE PROCESSOR CAN BE BEST DESCRIBED AS 3GHZ *4 CORES!

WHERE EXACTLY IS MULTICORE TECHNOLOGY USED AND HOW MANY CORES ARE ACTUALLY NEEDED FOR WHAT?

-FOR DAY TO DAY BASIC USE  OF A MACHINE(COMPUTER OR A SMARTPHONE)
A DUAL CORE PROCESSOR IS SUFFICIENT BUT OF A BIT HIGHER FREQUENCY IS SUFFICIENT.
ABOUT 1.4 GHZ FOR A SMARTPHONE
AND ABOUT 2.2 GHZ FOR A DESKTOP COMPUTER
-FOR HEAVY MULTITASKING AND GAMING A QUAD CORE CPU IS A MUST
 TO HANDLE THE HIGH LOAD WHICH CAN BE EFFICIENTLY DISTRIBUTED OVER THE 4 CORES.FOR THIS TYPE OF USE A QUAD CORE IS SUFFICIENT
FOR HEAVY MULTITASKING 
1.7GHZ QUAD FOR A DESKTOP COMPUTER
1.5 GHZ QUAD CORE FOR A SMARTPHONE
FOR GAMING IT FURTHER DEPENDS ON THE GRAPHIC CARD THOUGH CONSIDERING A DECENT ONE
3 GHZ+ QUAD CORE FOR PC
2.3GHZ+ QUAD FOR A SMARTPHONE

NOW LETS MOVE DOWN TO MULTICORES IN SMARTPHONES

WHEN IT COMES TO SMARTPHONES WE OFTEN SEE THE TERM CORTEX

ITS THE TERM USED TO REPRESENT THE DESIGN OR THE TYPE OF CORES

LETS LOOK FORWARD TO THESES TYPES:

32-BIT:

CORTEX A5:THIS IS THE MOST BASIC TYPE OF CORES AND IS OUTDATED MOST OF THE PHONES DONT EVEN USE IT IN THESE DAYS

CORTEX A7:THESE TYPE OF CORES ARE FOCUSED TOWARDS POWER SAVING RATHER THAN PERFORMANCE BUT THEY ARE BETTER THAN A5s

CORTEX A9/SCORPION:

THESE WERE MOST COMMON AND RELIABLE DESIGN OF CORES IN THE LAST 1-2 YEARS

THEY FOCUS MORE ON PERFORMANCE RATHER THAN POWER SAVING

SCORPION:IT IS THE ENHANCED VERSION OF A9 BY SNAPDRAGON

CORTEX A 15/KRAIT:

THESE CORES ARE WIDELY USED NOWADAYS IN HIGHER END PHONES.THESE FOCUS HIGHLY ON PERFORMANCE ABOUT DOUBLE THAN CORTEX A9

KRAIT:IT IS THE ENHANCED VERSION OF CORTEX A15 BY SNAPDRAGON

64 BIT:

COREX A53:

IT IS ENHANCED AND 64BIT SUCCESSOR OF CORTEX A7

CORTEX A57:IT IS ENHANCED AND 64-BIT SUCCESSOR OF CORTEX A15

CORTEX A72:IT IS CONSIDERED TO BE THE BEAST OF ALL AND GIVES DOUBLE PERFORMANCE THAN A57

SO THIS IS WHAT EXACTLY MULTICORE PROCESSOR ARE IN BRIEF .HOP THIS HELP U TO CHOOSE THE BEST PROCESSOR FOR YOU!