How to add 2d sprites in 3d unity

I want to add a 8 bit sprite into a 3d voxel game like infiniminer.
Like literally flat 2d no model maya or anything like that. just how do i add it as a 2d image in a 3d game with nothing else on it? is there any tutorials out there?

Use a quad object (or plane but quad is better) and apply a texture onto it. It is like the old way of Unity to make a sprite.

GameObject > Create Other > Sprite
You have to have the imported texture assigned as sprite (not Texture or GUI etc)