(Closed) How to create a solid ground for ridgidbody?

Sheer absolute noob question here but I am even struggling to create a solid ground.
Any tutorials or advice will be much appreciated

All I am doing is dragging a prefab onto a scene.
I am adding a rigid body and also a box collider, my noobness thought that would be it, but no.
Tried a quad and a collider on that and wondering is there some sort of reference if colliders are solid?

So anyway ignore all I say and let me start from scratch, but what is the best way to add a basic flat ground at 0 with a player object and rigid body that doesn't fall through infinity

Then after that I maybe back to ask more equally stupid questions about terrain creation

 

Ok dunno what I was doing before but just added the terrain package which is a leap ahead.
Added a box collider and now not falling forever ?! Dunno what I was doing wrong, but hey