Every single object is either a solid, a liquid, a gas or some combination of the three. Some things can move between states, and some can’t. Your bookcase is going to remain a solid, for example, but water changes depending on the temperature.
But a block of water ice still has the same chemical makeup as water in its gaseous form (steam). So what’s the difference? A solid object stays the same shape and takes up the same amount of space, or volume. Liquids take up the same amount of space but adapt to the shape of a container, while gases expand. But to really see the difference, you’d need to check things out at a microscopic level.
If you looked at water in its various phases under a powerful microscope, you would see that the particles in each behave very differently. When it’s a vapour (ie steam), the water particles vibrate and are moving very quickly. They’re loose and slide freely around with no particular arrangement. In comparison, liquid water particles also vibrate and can move around easily, however they’re more tightly packed and don’t move anywhere near as fast as their gaseous counterparts.
Finally, a block of solid ice doesn’t move (that is, the particles still vibrate but not enough to go anywhere). This is because its particles are tightly and rigidly packed together in an ordered pattern.