Newbie building a PC,please help

[Devildervish]

So foremost,I'd like to thank you for your consideration in visiting this thread.After initially thinking of buying a new desktop(for gaming) and visiting many marketplace threads,I've decided to buy individual parts to build it myself.But there are many unknowns I'd like to know to avoid making a mistake I would regret...

Motherboard:

CPU:There are CPUs which are have the extra K letter,meaning that can be over clocked.is it possible to give a scenario when over clocking is required?how important is over clocking as I have not done it since my years of gaming on the computer.

RAM:Other than the frequency 1333 1600 2133 2400 from which I've heard doesn't make much of a difference,there's this DDR value which ranges from 2-4.From an article I've seen online,the DDR4 ram which is to be released is going to be much faster and cooler to run.
It is supposedly said that it is better to run multiples of ram instead of single rams?eg. 4x4gb>>2x8gb

SSD:Is there a way to determine how fast or efficiency an SSD is?Im confused because there quite a variation of prices between different models of the same size(256gb)
Samsung 840 pro >> $200
Ocz vertex 4 >> $400

GPU:I've seen people's rig attached with two graphics card,what's the purpose?

PSU:
How do I choose an appropriate PSU?Ive heard about the bronze silver gold rating relating to the electrical efficiency and calculating the total power required.Is a high power value always better?

Misc:
(1)Any specific qualities or function which is good in these components?

(2)Is it possible that a component would not be compatible to another(function wise) even if they are able to be attached together?how do you tell so?

Thank you very much for your help
Ps. Might be adding more questions when I think of it.

 

[PhatLloyd]

You have really thought all possibilities through when asking this! Okay, where to begin.

Overclocking: Mostly overclocking is used to get more speed out of your cpu, eg: run a game faster or to process applications faster. Overclocking is for more "experienced" pc users and is not that important for the average gamer.

RAM: This far I'd say DDR3 is the best as you don't need to give your whole wallet for 2gb of DDR4. DDR4 is out but still most gamers use DDR3. And yes it would be better to use 4x4gb to make use of dual channeling.

SSD: I'm in the dark when it comes to this, you might want to post this as a separate question.

GPU: Using 2 gpu's increases graphics power and games which use crossfire will obviously run better. An article concerning that can be found here: http://computer-peripherals.yoexpert.com/video-and-graphics-cards/what-is-the-purpose-of-dual-graphics-cards-3165.html

PSU: Usually any psu over 600w should suit any pc, unless you run some monster with 10 hdds. You can purchase meters which test how many watts your pc uses. Higher is not always better. Imagine your pc as a rock (don't laugh) and water for electricity. You want just enough water (electricity) just to cover the rock, but not to much so that the rock starts to erode. So too much power can decrease life span.

MISC 1: Choose a good brand psu. Make sure you get the same frequency RAM. GPU is better for gaming, but don't neglect the cpu.

MISC 2: Usually if a part fits, it should be compatible. That's not always the case though. If you're uncertain post another question or pm me.

Longest answer I ever done!

 

[Zerk2012]

A few points, your motherboard determines the memory DDR 3 or 4 nothing else. For dual channel memory get 2X4 gb set not 4X4 or 2X8 if you need 16gb.
SSD's are so fast about any will perform the same unless your just into running benches. They make everything load faster your PC will boot up and be ready to use in about 15 secounds.