The Material Plane--the land where all mortals dwell--is a flat surface bounded on all four sides by the Elemental Planes: Fire to the west, Water to the east, Earth to the north, and Air to the south.
Unfiltered magical energy runs throughout the Material Plane in metaphysical rivers called ley lines that reach most corners of the known world, though they concentrate magic even further in certain locations. Other, more magical planes like the Feywild exist in parallel with the world of the mortals. Gods observe the world from their perch in the Outer Planes and occasionally even reach through to contact particularly devout mortals.
See
Magic Rule Changes from Standard 5e for more information on magic.