Relations and general structure of a game?

Newbie & Debugging Questions
#1

I’m done with my school project now and I figured I should start with a new game. A little more advanced this time (realistic physics etc).
But I’m not sure of how to structure it.

I started with two classes. GameLoop and UpdateRender.
GameLoop has an UpdateRender object to call for updates and renders every cycle.
Then I started thinking of everything else I need. Like physics and movable stuff.
Should all classes affected by physics be objects in the physics class? Or should I make physics an abstract class that the classes implement? Or something completley diffrent.
I have looked around for class diagrams or similar but haven’t found anything useful. Might be bad google skills, idk.

If someone could give me some basic guidelines I would be really grateful.

EDIT: I should probably add that I’m not using JOGL, LWJGL or something like that… If it’s relevant.

#2

I would suggest that you do a few more simpler games before jumping into games with Physics and that.

#3

I have done some simple boardgames/puzzles but I like bigger projects because it’s very easy for me to absorb information.
Therefore I feel that knowing “as little as possible” before starting something would benefit me more than if I already knew how to do most of something.

(Im really bad at explaining stuff -.-)