Its hard to build a computer if you know little about them not because its hard, its not really, but because you need to know what all individual parts do, what is cost effective, and what is compatible while what, and also how much do you want to spend. No matter your answer building a PC is still more cost effective then buying one. As an example I build my intel based computer using $1,800 AUD (Australian dollars nearly equal to American dollars) and it runs FTB Unleashed max settings far render distance at 200 FPS (limited to 200) while running my FTB server on the same PC and media server while playing media files from it also. it took 120 "NUKES" to lag the server even the slightest, didn't disconnect the server just lagged it.
One thing to keep in mind is bottle-necking. if you have a GTX titan graphics card but only a i3 CPU it wouldn't run up to standards as the graphics card would be waiting for the CPU to make certain calculation. it wouldn't drop it to the speed of the CPU but it does hinder it noticeably.
I would start by determining if you want an Intel based M/B or MSI. Intel products are more expensive but also has better support and work much better when paired with other Intel products where MSI products are good for 3rd party modified products, like ASUS. making it a bit more varied but usually just boosting low end products so they are usually cheaper. Also although 4th gen Intel products are just released I would not buy them and stick with 3rd gen instead. 4th gen isn't just twice the price it also has only a slight increase in performance then gen 3 products.
After that you want to get your CPU. I will use Intel products as an example as I have more experience with them. your CPU is Primarily used for calculations so things like video rendering will be heavily based of your CPU. since you don't know to much about computers i suggest getting (if you choose Intel) one with the K suffix, this means it's pre-overclocked. T suffix is power saver but reduces performance I suggest staying away from these ones. for the amount of cores you want, getting more then 4 cores is nearly pointless, there is hardly any programs/games that benefit from more then 4 cores so you do want 4 cores, but don't take CPU's with more then 4 cores as a priority. Also the speed you want is measured in Ghz. to not go into to much details you can just say that the Ghz x number of cores = total speed. (This is completely vague and not accurate but its the best representation for someone with no computer knowledge) the most cost effective would the the i5's as the i7's are ~ 25% better but cost double or triple. Also make sure its memory type is 1333/1600 (this is the speed of the ram it supports).
Now on to ram, contrary to popular belief, size of ram is NOT the most important thing, speed is. you want to make sure to get DDR3 1333 or 1600 then look at the size, if you have a 32bit OS the max ram it supports is 4Gig everything else is wasted, so make sure to get a 64bit OS as it has a lot more benefits over 32bit OS, not just increased RAM support.
If you want gaming you need to get a graphics card, make sure you have a Motherboard with pcie (pci-express) x16 bus available as all the good graphics cards need at least x8, but since its no extra cost for x16 might as well get it for future compatibility. As for the graphics card itself its hard to determine what you need, just MAKE SURE its current gen, DDR5 RAM, and depending on how many monitors you want and if your extending displays or not, you only need 1Gig (2 to be safe) when using 1 or 2 monitors, but if you want to run something like eyefinity gaming you would need 3Gig or more depending on the resolution, might even need 2 graphics cards hooked together in SLI or Crossfire (its just joining 2 graphics cards together to make it act like 1 super one). apart from that 2gigs ram is more then enough just again makes sure its DDR5 and current gen.
The power supply you don't need to worry to much about, just make sure it has the right connections for your M/B (connections for certain graphics cards can be bought separately and don't need to worry about). Computers don't take as much power as people think, all you need to do is make sure its at least 350watts, try for 500-550watts with a graphics card to be safe. the gold rating ones are the best but don't need to worry to much about it, if you want a very clean set up the full modular power supply allow you to take out unused cords from the power supply but they cost a bit more.
as with monitors, mice, keyboards, speakers etc. they are all personal preference, just make sure to get monitors with the ports your graphics card has. Try and get one with DVI or DisplayPort. HDMI also works but i wouldn't recommend it.
hope I helped
