Solids are used where we need something to keep its shape or to support something. This is because they keep their shape, stay where they are put and cannot be compressed.
Do not keep their shape, they take the shape of the container thay are in
Cannot be compressed (keep the same volume)
Liquids are used where we need something to flow e.g. for making a drink, or when we need something to take up the shape of a container such as a mould.
Do not keep their shape, they completely fill the container that they are in
Flow, spread out quickly from where they are to start with (this is called diffusion)
Can be compressed (squashed into a much smaller volume)
Gases are used when we need something to spring back after it has been squashed e.g. in a tyre or when we need something to spread out e.g. fly killer spray.