Cant Understand Materials


I have recently started using Unreal Engine. I am working on 4.18.1. And it seems i can’t really understand materials. The images attached will help you understand what’s happening in my case. Few details are

First i created a terrain
Then i selected a material for landscape from my files
when i apply the material to the terrain, the terrain material in details TAB and the material in Content Browser Tab both went empty.

I dont know why this is happening, please guide how can i do this. I would appreciate if anyone can provide a link for a complete terrain tutorial as well.