Humans developed to function in a three dimensional world where we see larger objects like bricks and planets. That’s why classical Newtonian physics seems plausible to our mind and senses. On the very, very small scale of quantum mechanics our intuition and senses are inadequate. Quantum mechanics does not explain everything. There is no quantum theory of gravity yet. But what the equations of quantum mechanics do is describe the behavior of the subatomic world to a great degree of accuracy. That allows the possibility of quantum computers operating at speeds orders of magnitude faster than we can imagine using nonlocality, that is quantum entanglement. There are other interpretations besides the multiverse of what is going on “behind” the equations. Many good general readership books on this subject.