First, quantum mechanics is the study of the subatomic world. Our current best description of what happens on the inside of atoms. The easiest way to dip your toes into quantum mechanics is by understanding the history of gravity and the wave-particle duality debate.
Before Newton, we described falling objects and celestial motion as separate things. Newton’s brilliance was unifying gravity as a universal force governing both apples and planets. He gave us precise math that let us eventually land on the Moon. Einstein came along and replaced Newton’s force with a property of space itself. Gravity is the curvature of space-time and everywhere all at once.
As good as Einstein’s theory is, it is not perfect. His model failed at the subatomic level. Quantum mechanics emerged to describe small-scale stuff, but this era is filled with speculation. Our observations are confirmed. In life, we understand well how a rock causes ripples in a pond, as well as how bullets from a machine gun fly through the air hitting and passing between things. At the subatomic, it’s kind of like a spread of bullets acting like a wave. That’s weird.
This all started with debates as to whether light is a wave or a particle. Decades later the debates spread to all subatomic particles and atoms, not just massless particles like photons! I have no doubt we will unify our descriptions. Afterall, they are only descriptions, not reality itself. We are simply looking for a way to describe and predict well.