Man , Just calm down. Everything is totally fine.
You said you're a complete beginner , so let me tell you some stuff first.
The screen you get when you press Volume Down and Power is the bootloader screen.
and TWRP (TeamWinRecovery Project) is the recovery. (Duh)
well the phone is split into partitions. You can say that the main partitions are for the system , data, recovery, kernel.
from what you've just said your system partition is empty. your recovery partition has a recovery installed , and the kernel cannot be empty so there's a kernel on it.
You get NO OS installed because the system partition is empty. and you get the root question because your phone doesn't have an operating system installed therefore it is not rooted.
Try clicking install zip from TWRP , if you find something on the sdcard that has a ZIP extension and that looks like a phone ROM (a firmware AKA the operating system) then flash it.
If the sdcard is empty then you have two choices
1) Flash the phone back to stock firmware
2) Flash a custom ROM on the phone.
Flashing a custom ROM will be easier for you since TWRP is already installed.
to flash a custom ROM , there are many detailed guides on XDA teaching you how to do this. But I'll tell you how to do it in a short non-detailed way.
The first thing you need to do is download a ROM for the phone. Go to the "One X+ Android Development" or "One X+ Original Android Development" sections of the forum in order to find a custom ROM that suites your needs.
Then you need to copy the ROM to your device , but since your device cannot turn on into system you can go to Recovery and push the ROM onto your sdcard . To do so , you need to :
1) Set up ADB on your computer (Search how to do that )
2) Push the rom ZIP file by using the command "adb push ROM.zip" (Replace the word ROM with the name of your ROM file.)
After pushing it into the sdcard you can flash it from recovery (Install it). If it doesn't boot after flashing then it is because you need to flash the kernel that comes with the ROM.
To do that :
1)Set Up Fastboot on your phone (usually comes with ADB , there are many tutorials on how to do that. )
2) Extract the ROM zip file using WinRAR or WinZip.
3) Open a command prompt
4) CD (Change Directory) into the destination where you extracted your ZIP file.
5) Reboot your device into Bootloader.
6) Connect it to your computer (duh)
7) Flash the kernel by using the command "fastboot flash boot boot.img"
then reboot your phone and it will hopefully boot into the system
I hope I helped , If you have any more questions then feel free to ask
and If you couldn't do this then I can connect to your computer on Teamviewer and help you set ADB and fastboot up on your computer
Oh , and to make flashing the kernel easier you can use hasoon2000's toolkit. It might help you a little
Check it out : http://forum.xda-developers.com/show....php?t=1994961
Please Press The Thanks
button if I helped. It's free. I promise!