It should be noted that quantum physics is a super broad term. You might as well be asking "explain math". Quantum physics, better known as quantum mechanics, deals with stuff that happens on a really small level. I'm talking microscopic interactions. Quantum mechanics is meant to fill some holes in traditional physics. For example, light is both a particle and a wave. It has properties like a wave, but it also has properties like a particle. The particle in question is called the photon. It also has energy of its own, which is an important trait.