To access your material editor you can use the shortcut key “M” or select the materials button on the top ribbon. 
There are 2 different material editors available for use. The scary looking one (Slate material editor) and the not so scary looking one (compact material editor).
When I was learning how to edit materials and apply them I found that the scary looking one was actually very easy to use and also fun. I don’t really use the not so scary looking one as I find it more fun dragging and dropping my materials onto my objects as well as just being able to drag a .bmp onto the slate editor (from windows file explorer) for texture mapping.
Visually you are able to see in an instance how your material has been mapped.
On the left-hand side of the dialog box is the Material/Map browser. In this section of the slate material editor interface, you are able to find materials either by typing in the name or browsing through the materials.
Something to note. Not all materials are compatible with each renderer. If you change to a renderer and you have materials in your scene that are not compatible, an error message will pop up and an approximation will be used. For best results, I would suggest using materials that are compatible with the renderer.
For instance, if you are using the Arnold renderer then you should use Arnold materials. Physical materials do not work with the Arnold renderer.
