If you want to use multiple materials on a single model (for example when making a tabletop out of glass and the frame out of metal) you have to use material ID’s. Polygons on a model can be assigned a material ID inside the modeling software, these material ID’s represent the parts (or elements) of the model that will have a corresponding material assigned to it inside the engine. Setting up material ID’s is pretty easy, just Google the steps you have to follow for whatever modeling software you’re using (Maya, 3ds Max etc.).
More info on this:
https://docs.unrealengine.com/latest/INT/Engine/Content/FBX/Materials/index.html
By the way your link has a typo at the end, here’s the working version:
So how do you make it look more realistic? Well first you want to get a basic understanding of how materials and PBR work in UE4. There’s a lot of videos about this on Youtube and there’s extensive documentation on the official Wiki.
Basic material and PBR info on Wiki:
https://docs.unrealengine.com/latest/INT/Engine/Rendering/Materials/index.html
https://docs.unrealengine.com/latest/INT/Engine/Rendering/Materials/PhysicallyBased/index.html
Useful video on PBR:
I highly suggest you check out the UE4 library inside the launcher and look for the free available content such as the Sci-Fi Hallway. Most of these projects contain a lot of materials that you can open and study to reveal how they work. A lot of the stuff that you will encounter when making materials has been well documented and can easily be found using the UE4 Wiki, Google and YouTube.
The engine also comes with starter content that contains many basic materials that you could check out. Just open the content browser and look for the ´StarterContent´ folder. If you don´t have this folder simply create a new project and make sure not to uncheck the ´include starter content´ stuff.
edit:
I keep saying UE4 Wiki but what I mean is the official documentation: