Classical mechanics is the branch of physics that deal with the things that we can see in everyday lives such as movement of cars, trains, bullets, and planetary bodies in the universe. It is also known as Newtonian mechanics.
Quantum mechanics deal with properties of things that are as small as size of an atom or electrons. At such small scale, the movements and behaviours of the particles will be markedly different from the things that we saw in life. Quantum, nuclear, and particles physics are all under modern physics.