Unity seems to be in 2D, but I want it in 3D

I attempted to add a texture to the terrain, but the splat is not there. Instead, None (Texture 2D) is there. I have materials I want to use, but it won’t let me navigate to them. What am I doing wrong here?

Unity seems to be in 2D, but I want it in 3D

if you’re talking about the default scene mode:

edit > project settings > editor there is a point “Default Behavior Mode” which you can set to 3D

I attempted to add a texture to the terrain

if you’re talking about the unity terrain object/component, you can find an instruction here: http://docs.unity3d.com/Manual/terrain-Textures.html

it shows how to add textures to the terrain mesh. there are images too.

you can add the textures via drag and drop. they don’t need to be materials. the images need to be set to “texture”, make sure they are not imported as “sprites”

edit
since you accepted the answer without understanding it (you posted the same question again)
i made a small video, which should show it to you: (click on this blue text)