The explanation of how gravity operates is still a theory, even though the presence of gravity is very clearly observed.
I have never gotten a clear explanation of the cause of gravity although as you say it ''is very clearly observed''.
I asked a neighbor friend to explain what caused gravity and he said it was the spinning of the earth. I said that didn't seem right, that a spinning tire throws mud off. It doesn't hold it on. I have a son who is a bona fide genius in many things and he attempted to explain it but really it amounted to "we don't know for sure".
Gravity is a force of nature and is a good example to give an atheist that doesn't believe in something he cannot see. You can bet your a$$ he believes in gravity.
Gravity is not tied to the spinning of the earth. It's tied to mass density. Mass warps space, and greatly massive objects warp space a lot. The warpage of space around massive objects causes other massive objects to be drawn towards them, just like if you spread a thin rubber bladder over a frame creating a large flat surface and then place a heavy steel ball in the middle. then put another smaller steel ball on it, and it will be drawn to the more massive one (or, rather, they will be drawn together, but due to the dramatic difference in mass, the less massive object will appear to be moving towards the more massive object). You can even place the small ball into orbit around the much more massive ball by the way you start it on its course.
The above is a three dimensional model of a four dimensional phenomenon. The operation of gravity involves a fourth dimension, and we cannot perceive a four dimensional model, so there's no way to show it to anyone in a way that makes the operation of gravity intuitively obvious.
