Matter generally occurs in three states:
1) Solid (2) Liquid and (3) Gas
They have definite shape and volume. The atoms are closely packed together. They vibrate about a fixed point but do not move (i.e. the particles of solid).
They occupy the shape of the container. The molecules and atoms of liquid are loosely held and so they can move or flow. They have no definite shape but have a definite volume.
They occupy the whole volume of the container. They, are held by negligible forces and so can move randomly in any direction. NB: Evaporation, sublimation, melting and freezing are all changes of states.