GASES eg the air mixture around us (including the oxygen needed for combustion) and the high pressure steam in the boiler and cylinders of the steam locomotive. All of these gases are 'invisible', being colourless and transparent, so note that the 'steam' you see outside of the locomotive is actually fine liquid droplets of water, formed from the expelled steam gas condensing when it meets the cold air - the 'state change' of gas to liquid (same effect in mist and fog formation).LIQUIDS eg water is the most common example, but so are, milk, hot butter, petrol, oil, mercury or alcohol in a thermometer.SOLIDS eg stone, all metals at room temperature (except mercury), rubber of walking boots and the majority of physical objects around you. In fact most objects are useless unless they have a solid structure!
Solids do not diffuse (no intermolecular space).
Liquids diffuse sometimes (miscible liquids do ) but other times , they don't ( immiscible liquids do not) due to some amount of intermolecular space.
Gases diffuse readily ( large intermolecular space).