Good on you for not using toolkits. First make sure you have the correct drivers installed, as well as latest versions of adb and fastboot. Then you have to unlock the bootloader (wipes your device). Go into bootloader mode either by using the command 'adb reboot bootloader' (with usb debugging enabled) or by switching your phone off, holding both volume keys then pressing the power button. Then use the command 'fastboot oem unlock'
Next flash a custom recovery. (I suggest TWRP as it has root function built in and seems to work best.) 'fastboot flash recovery "nameofrecovery.img"'
Then boot into your custom recovery. From there reboot to system and TWRP will prompt you to root your device, alternatively you could sideload supersu
http://download.chainfire.eu/382/SuperSU/UPDATE-SuperSU-v1.93.zip.