Well, I'm not the best at creating low budget systems, but these guys are. Also save your money, odds are once you go down this path, you'll want to upgrade somewhere down the line. These are excellent starter builds, you can save some money off of them by not buying the SSDs
$899 -
http://www.maximumpc.com/build-it-overclocking-in-a-budget-gaming-pc/
$861 -
http://www.maximumpc.com/maximum-pcs-budget-gamer-build-for-may-2015/
This one is one of my own creation, but like I previously said, the first two were built by pros. (also, the mobo isn't designed for overclocking hence the H97 rather than Z97) The 270X is actually quite overkill for CSGO, it was my first GPU prior to my GTX 980. The Pentium K is an amazing processor for so little money. As for installing the OS, just burn it to a clean flash drive and do it that way or you can scratch a few extra dollars for a disc reader. Good luck, never be afraid to ask for help
$687.64 -
http://pcpartpicker.com/p/NVTQsY