Matter is a substance that takes up mass and space. Chemistry is the study of matter. Whilst heat and light aren't classed as matter, they are also studied in chemistry as their properties have dramatic effects on the behavior of matter. Matter is in one of two states - physical or chemical.
A chemical reaction is when the chemical properties of substance are changed by the rearrangement of atoms within the substance. Chemical change is the transformation of one substance into an entirely new substance. Chemical change requires and involves a chemical reaction. Water can be changed by the use of electricity into its component parts, hydrogen gas and oxygen gas.
Chemistry focuses on the interactions between the different types of matter whilst physics leans to focus on the nuclear and subatomic region. If you understand chemistry, you can better understand the world around you. Whenever you cook, you are actually using chemistry. Anything that you can taste, touch or smell is a chemical. Why does one headache tablet work better than another, why does soap lather more in hot water? It's all in the chemistry!
Chemistry is most commonly seen in medicine and the sciences. Many fields of work require some understanding of chemistry. This is true of biologists, physical therapists, dentists, nurses, plumbers, veterinarians, doctors and many more. If you have a basic understanding of chemistry you will understand more of the world around you and it may also be very useful in a future career choice.