Physics can be divided into two broad areas: classical physics and modern physics.
Everything physics discovered and created until the late 19th century is part of classical physics. By this time physicists believed they had already discovered everything! They were very pleased with themselves.
However, in the early twentieth century, phenomena involving high velocities, close to the speed of light, and discoveries related to very small structures (such as molecules and atoms) led to the development of relativity and quantum mechanics. It was the modern physics that was born.
In high school, you may learn notions of modern physics. For now let's study only classical physics. Everything you will study in this area is part of classical physics. It is divided into the following parts:
Mechanics: studies the movement of bodies. Everything that moves is the object of study of this part of physics. To understand the motion of stars, planets, cars, people, etc., we need to understand the mechanics.
Thermal physics: studies the heat and temperature of bodies. Why does the ice melt? Why do some clothes make us warmer than others? Why is it better to bring drinks to the beach on a Styrofoam? These are some questions answered by thermal physics.
Optics: studies the phenomena related to light. What is the rainbow? Why do bodies look bigger when viewed through a magnifying glass? What are eclipses? How does our vision work? You will get answers to these questions by studying the optics part.
Wave: study the waves. We are surrounded by them. Let us understand better the waves of the sea, the sound, the musical instruments, the radio waves (including television and cell phones), the microwave operation, and so on.
Electricity: studies all appliances that heat and move using electrical energy. The operation of "plugged in" or battery operated devices will be more readily understood after studying electricity.