The four states of matter are:
In a gas, the atoms are randomly flying about colliding and bouncing off each other and whatever else is available. The hotter the gas, the more energetic the molecules move and collide.
Plasmas exist at very high temperatures, such as those in stars, electrons may be stripped from nuclei and the nuclei which then move through the "electron sea". In a way a plasma is a gas with electrical characteristics (e.g. it conducts electricity).
A liquid is a collection of atoms that maintains a fixed volume but adjusts to the shape of its container. The atoms are often held together by attractive forces between molecules
A solid is a collection of atoms that maintains its shape and volume. If the atoms in a solid have a repeating arrangement, they form a crystal. If they are arranged without a pattern we call them amorphous (glasses). A third type of solid is a plastic, which can be formed into any shape and is made of long molecules called polymers. Plastics are relatively recent discovery, and are only a few decades old.