Genesis 1:6 - Waters

I actually don't grasp this, I even took a sneak peak at the next passages.

And God said, Let there be a firmament in the midst of the waters, and let it divide the waters from the waters.

The waters? The oceans? Water in the sky and water on the planet Earth? Can it be something about the whole planet consisting of waters and gases, high up into the atmosphere? That it really was no seperation between the sky and the planet itself?

Had God already created Water? It is not mentioned earlier, but perhaps hinted to in Genesis 1:2 - that God was hovering above the waters - but still, it isn't said that he actually created water. Still, he could have made water, earth, gases, rock and everything else in Genesis 1:1 already, just that it isn't mentioned specifically.