Physics studies everything that happens in nature. Generally, we can narrow it down to the study of energy and matter. This description might sound a little vague but that is just how wide the reach of physics reaches. It is basically anything we can think of that does not involve human interaction or intervention. We use mathematics in physics in order to quantify these phenomena and predict other phenomena accordingly. Some branches of physics include:

Classical Mechanics - the branch of physics involving the movement of everyday object under applied forces and given energies

Quantum Mechanics - the branch of physics that deals with how very small particles like electrons and photons behave in very small scales. We have this distinction from classical mechanics because, on the quantum scale, not all of the classical physics laws hold up or are directly applicable.

Electromagnetism - the branch of physics that deals with electronic interactions, especially with electrons and protons. Electric fields and potentials of different charge distributions come into play here.

Thermodynamics - the branch of physics that allows us to study anything involving temperature. Not only that, this study goes way into the particle scale to explain thermal phenomena.

Relativity - the branch of physics that governs the behavior of any object that manages to move at speeds approaching the speed of light.

These are not the only branches of physics but these are pretty much what is usually covered in school if we just consider fundamentals. The more advanced in physics we go, the more we see that we can use more than, or even all of the branches of physics in cooperation with each other to describe phenomena.