In that case I personally would recommend you to just copy some assets from the demo projects into your own one + start creating a level. Over the time you will get better and better. 
-> after that you know how to use the light/material/post process/level design system. After that you can do it with your own assets
Some useful documentation pages:
https://docs.unrealengine/latest/INT/Engine/Rendering/PostProcessEffects/index.html
https://docs.unrealengine/latest/INT/Engine/Rendering/Materials/index.html
https://docs.unrealengine/latest/INT/Engine/Rendering/LightingAndShadows/index.html