Gas is just a state of matter. If you cool oxygen or hydrogen enough, you get liquid oxygen and liquid hydrogen. If you heat steel you get liquid steel. You can even vaporise it if you get it really hot.
Remember you have the three basic states, solid, liquid and gas. To make something go from a solid to a gas requires adding energy (heating) and to go the other way you remove energy (cooling).
Everything is made of atoms and the amount of energy those atoms have decides what state it is. Oxygen and hydrogen alone need far less energy than water to be a gas, but combine them and they suddenly need a lot more energy. Give water enough energy and it turns to steam, which is also a gas.
So water being made of hydrogen and oxygen is no more unusual than wood being made of carbon and other atoms.
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