States of Matter
Matter can be divided into three groups - solids, liquids and gases, depending on their states.
If you move a piece of wood or a book from one place to another and press it with some force, you will see that neither its shape nor volume changes. Such substances whose size and volume are fixed are called solid such as ice, brick, chair, book.
Liquids have definite volume but size is not fixed.
Molecules in gases are far away from each other as compared to both solid and liquid and the attraction force between them is almost equal to zero. So molecules can move more freely.
Change of State
Substances can also be changed from one state to another. For example, Water is a liquid state of matter. If we freeze it at a very low temperature then it becomes ice which is in solid state. If this water is boiled then steam (vapor) is formed which is gaseous state. On cooling the steam, water is formed again.
Thus, we see that ice, water and steam are different states of the same substance (water).