In looking at a drop of water under a microscope, we find there are twice as many H's as O's. I am not sure how clouds get formed. But the clouds know how to do it, and that is the important thing. Clouds just keep circling the earth around and around. There is not much else to do up there.
Water vapor gets together in a cloud.
When it is big enough to be called a drop, it does. Humidity is the experience of looking for air and finding water. Rain is often known as soft water, oppositely known as hail. Rain is saved up in cloud banks. In some rocks you can find the fossil footprints of fishes.