Hello, I am relatively new to the programming field (I have had some experiments in simple languages like Python).

Me and my friends are currently in the works of a project to create a game console (original games, that is). I have been assigned to create the operating system.

How would I go about doing this? If I left out anything else, please tell me.

Edit: This is going to be on a small microcomputer, probably an Orange Pi Lite.

I would choose the most supported operating system for the device. 

"Creating" an operating system is a whole other box of nails.  If that's what you really want to do, then I would suggest seeking out a forum and some extensive documentation about operating system design and programming, and then enroll in college to get a few degrees in computer sciences before beginning.

It looks like according to the sales page you can choose from: Android 4.4, Ubuntu, Debian, and Raspbian

The real question is what environment do your game developers want to work in?  These can all be considered Linux operating systems, however there are some significant differences.  I suggest you look into what those are and make your decision based on that.

Sounds like a fun project.  Good luck!

Septopus makes a solid point developing an Operating System is a complex task and is generally a project that is given to Graduate level computer science students.  This is a highly ambitious task for a new programmer

Septopus, I am trying to use Debian, but the thing is, I really haven't used and Linux distros in a long time. It's like trying to write an essay in Swedish. I'm just confused on how to make the GUI suitable for a game console. I would like it to look similar to Lakka, except Lakka is for retro games only.

P.S. about the computer science thing... I'm in an excelled high school so in 11th and 12th grade, I'll be enrolled fully in college courses. I also hope to go to MIT and take computer science as my major. I hope to create a business of of software and hardware.

Unfortunately while I do have extensive experience in Linux, none of it extends to GUI related topics.  I think Debian defaults to using Gnome for it's "window system" though, so I would consider writing a simple program that acts as the user interface for your gaming system.  Just write a regular application that will run on Gnome and will interface with the user for selecting and loading games.  Once a user selects the game they want to play, you launch it in a separate process and when that process ends, you either restart the GUI application or it stays in memory and is given back/takes back control somehow.

These are just some very very rough ideas of how I might try to proceed.  Like I said, my understanding of the X window system(what Gnome and KDE run on top of) isn't even rudimentary these days...