Texture Conversion Problem

Im just wondering how u convert a 2d or 3d texture to a UV map.
I asked gnomon how to make a starfield and they replied with this,

The best thing to do is to create a sphere, scale it up to about 400, and
apply a Surface Shader to it... Then for the surface shader's color, you can
map a Granite texture to it... Make the base color black and the 3 granite
colors can be yellowish, bluish and pinkish... Then you can convert the 3D
texture to a UV map and further refine it in Photoshop.

Pretty unspecific if u ask me, i think i got it for the most part. all i need to know how to do is convert a 2d texture, or 3d to a uv map. Please reply should be simple. Thanks in advace.