1. If you cannot find the cesium plug-in in the plug-in list, you need to go to UE4 mall to get the plug-in. Search Cesium for unreal in the mall
2. In the plug-in list, introduce the downloaded Cesium 
3, Add sky system and light source to the scene.
3.1 Several things need to be added to the scene: directional light source, BP_Sky-Sphere, and sky lighting. (Atmospheric fog)
Directional light sources and sky lighting need to initialize the coordinates.
3.2, add sunlight.
3.3 Settings Light
