how do you get the normals pointing inside of a mesh?

ok well i kinda want to make a sky within a cube. and when i go into uvmapping, from the inside of the mesh its clear therefore the normals are pointing outward. ok well how do i get them to point inward? or do i half to use a plane and make a cube out of it casue i know this works i did it. but the cube is easyer lol.

Go into edit mode. Select all the vertices and press W->flip normals.