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Astrophysical black holes are surrounded by accretion disks, jets, magnetospheres, and coronae consisting of magnetized relativistic plasma. They produce observable multi wavelength and multi messenger signals from near the event horizon and it is currently unclear how this emission is exactly produced. Magnetic reconnection and plasma turbulence are viable mechanisms to tap the large reservoir of magnetic energy in these systems and accelerate electrons to extreme energies. In some cases the electromagnetic emission is accompanied by a multi messenger signal in the form of neutrinos, cosmic rays, or gravitational waves. Modeling the emitting systems necessitates a combination of magnetohydrodynamic models to capture the global dynamics of the formation of dissipation regions, and a kinetic treatment of plasma processes that are responsible for particle acceleration, quantum electrodynamics effects like pair creation and annihilation, and radiation. I will present novel studies of black holes and how they radiate in regions close to black hole event horizon, using both first-principles kinetic particle-in-cell simulations and global large-scale three-dimensional magnetohydrodynamics models. With a combination of models, I determine where and how dissipation of magnetic energy occurs, what kind of emission signatures are typically produced, and what they can teach us about the nature of black holes.