How do Axes work in a 2D setting?

Hi to all,
I am writing because I’m a newbie to Unity and I am unable to find the answer to my question:
how do axes work in a 2D game project in Unity?
Okay, I did notice one person stating on this forum that Unity uses Y and Z axes for 2D games.
But in what order? that is: Y and Z describe bottom-up starting from bottom-left of the screen? How about the X axis? Does its origin start from bootm-left as well?
It looks like I’m moving my GameObjects around in the SceneView, but cannot find them back when I click on Play.
Please help.

X axis is always set as the screen width, and Y the screen Height. Z is used as depth for sprites rendering.