Unreal Engine 4 has five light types: Directional, Point, Rect, Spot, and Sky. Directional lights are primarily used as your primary outdoor light or any light that needs to appear as if it is casting light from extreme or near infinite distances. Point lights are your classic "light bulb" like light, emitting light in all directions from a single point. Rect lights are good for emulating lights with rectangular areas, like overheads or TV screens. Spot lights emit light from a single point, but have their light limited by a set of cones. Sky lights capture the background of your scene and apply it as lighting to your level's meshes.
Below you will find links to quick references for each of the light types.