Umbrakinesis is the ability to mentally extinguish visible light and surround oneself or others in darkness and shadow. One with this power could or surround foes in pitch black space making all light in that area stifled and the person unable to see around them. One with this ability can physically control a shadow by creating them where they should not exist or simply moving them, a power which on its own is very innocuous unless one is easily spooked or afraid of the dark.
Note that one with this power does not have the ability to animate the shadows into beings of their own physicality. They cannot harm tangible objects or organisms because a shadow is merely the absence of light. It is, itself, not alive nor can it be used as a weapon outside of its capabilities of removing light.
Few with this ability are gifted with the extraordinary ability to travel through shadows (called Umbrageous Teleportation, accomplished by deactivating light particles and converting said particles into a dark version of a wormhole) and even fewer shift into an alternate dimension.