First time building a PC need help

So this my first time building a PC and i have a few questions about setting it up

https://pcpartpicker.com/user/jalen793/saved/qnr323

this is my build and ive run into a dead end the motherboard has a 6 sided screw head that i dont have so i need to buy that. then i didnt purchase any fans or coolers as i dont know if its necesary. and how would i go about installing windows 10 i was going to buy a key on G2A but dont know what to do next

Naw, here, the 380 is a placeholder for the RX 480 at the end of the month, 750W PSU just incase RX 480 crossfire is decent

far as windows goes, don't buy an OEM key if you're going to buy a key because it only works once basically, and I'd probably avoid the grey market, as it'll all come crashing down at some point anyways
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Wait please don't tell me you actually bought those parts
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PCPartPicker part list: http://pcpartpicker.com/list/xTvQ7h
Price breakdown by merchant: http://pcpartpicker.com/list/xTvQ7h/by_merchant/

CPU: Intel Core i5-6500 3.2GHz Quad-Core Processor ($197.99 @ SuperBiiz)
Motherboard: MSI B150M Pro-VD Micro ATX LGA1151 Motherboard ($61.99 @ Amazon)
Memory: G.Skill NT Series 8GB (1 x 8GB) DDR4-2400 Memory ($29.98 @ Newegg)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive ($47.49 @ OutletPC)
Video Card: XFX Radeon R9 380 4GB Double Dissipation Video Card ($213.98 @ Newegg)
Case: Cooler Master N200 MicroATX Mid Tower Case ($42.99 @ NCIX US)
Power Supply: EVGA 750W 80+ Gold Certified Semi-Modular ATX Power Supply ($79.99 @ Amazon)
Total: $674.41
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2016-06-16 15:01 EDT-0400

yea i have everything already except windows 10

Check if the case that you got has any screws of the same size that came along with it.
About the fans or cooler,if you have the time and patience,you should go along and purchase a nice cooler ( I have the Cooler Master Hyper 212 Coolerthe choice is yours) or just go ahead and use the cooler that comes along with the processor. It's not the best thing out there,but I'm guessing you just want to get the system running.
As @Streetguru mentioned,it's worth just going legit with the windows 10 key,coz sooner or later,when major updates start rolling in,you will need not be bothered.

Microsoft Windows 10 Home 64bit Its only $83.89. One time install and forget about it. On the other hand,there's different OS's like Linux.

i dont understand how to go about getting windows can i do it once i boot up the pc? or do i have to get it on a usb somehow? and there is differences between buying it threw g2a i mean it said oem 64 bit? im sorry if i sound dumb, im just extremely new at this and would like to understand.

Well, how's the return policy where you bought them? you could have done way way better

All you do is burn a windows ISO to a USB using RUFUS, or if you just want things as simple as possible, buy a windows 10 USB

you don't want an OEM key

i dont really want to return anything unless it doesnt work im tired of waiting for the mail anyway

Well I'd suggest at least returning the GPU for the RX 480 shortly, it's 20% more performance, and 100% more VRAM at around the same price, in addition it has A-sync support when DX12 rolls around to gain even more performance compared to maxwell which has no A-sync support

and the PSU is really sub par, the CX series is super low end from corsair, not something one would normally buy

yeah with the power supply I'd try and get that changed ASAP.
Currently running cx series and it started going dodgy on me after 1 and half years. Your mileage may vary but just as an FYI

ill consider all this at a later time thanks alot guys u helped a ton.