You do this by clicking the green button that says 'Clone or Download' then selecting Download ZIP. This too it just a 'drag and drop' process so don't worry, I'm sure you can handle it. Since windows doesn't properly recognise the board, you should manually install the drivers. In this instructible I'll show you where to get the boards, how to program them and FIX the no USB connection problem so you can program it exactly like an Arduino, using just a USB serial connection. (A bootloader is basically Windows for microcontrollers, it doesn't do anything, but you still need it to run stuff) The boards can't be programmed over USB, since they don't come with a bootloader. You'll say it sounds too good to be true and it kind of is. The best thing (apart from it's amazing speed and overall performance) is the ability to program it with the Arduino IDE, essentially making it an Arduino. If you haven't heard there's an Arduino nano like board, nicknamed the blue pill. However if you need more speed, more analog inputs, more precision, but still don't want to switch from Arduino programming, there's a elegant solution.The blue pill!
You and I both love Arduino boards, from the smallest Attiny85, to the biggest MEGA2560.