Why does youtube make my videos narrow?

When I started making videos of ps3 gameplay for youtube I ran into a massive problem, when I uploaded them to youtube they became really narrow and U-G-L-Y, they ain't got no alibi (o_O!)
They looked horrible, and ain't no one wana watch poor quality videos!
So i typed some stuff into google such as:
What is the best camera to capture gameplay for youtube?
Why does youtube make my videos narrow?
How to make good quality videos for youtube.
And it was a fucking mess going through all the bullshit! It was specs this and specs that and format this and edit that, why all the bullshit? Why couldn't I find an easy answer (^_^?) Why? Because people are stupid, END!
So friends, here is the EASY answer to the narrow video problem. It's the resolution of the video. My camera was filming in 640x480, and it's too low. So I thought about buying a new camera, but I'm at uni and that's just not in the budget these days, SO, I thought hang about! My phone has a camera in it, I have a galaxy S4, damn thing is better than my digital camera! It can record in full HD! but I was worried about the file size, so in the settings I changed it to 1280x720, It's fills the youtube frame perfect! Has good quality and sound and the files aren't too big! Awesome, it's set! BUT, how is the phone gona stand up while I'm gaming! It gona fall over! Well I built a simple little holder for it, and as you can see it's just four screws in a bit of wood with some plastic twine for extra support.
Now I get good footage of gameplay and that's that, I hope this helps if you've had the same problem!