Scratch

I think the current X-Y could not be changed because it would mess up lots of projects, but here's my definition on X and Y.

X means left-to-right, and Y bottom-to-top.
X position 0 and Y position 0 begin at the center of the screen.
If you use the "change X by (10)" block on a Sprite, it will move 10 pixels to the right. Pixels, if you don't know, are small dots on your screen that you see if you look close up.
How would you make the Sprite go left? Change the (10) to (-10) (see the minus sign?) That means 10 pixels left.
With Y, numbers above 0 mean up, and ones below 0 mean down.

One other thing is the "go to X: (0) Y: (0)" block, which in my terms moves your Sprite back to X: 0 Y: 0, (the center,) and then moves it's X and Y to whatever you typed in to the two slots.

You can also move your mouse around the Stage and in the bottom right corner you see your mouse's X and Y, which can make finding positions easier.

That concludes my lesson on X and Y!