UV Mapping problems using an imported .mhx file

I have been trying to UV map a character imported as an .mhx file in blender. I used makehuman to create it. I deleted the old textures so I could put in my own. But when I get the UV map exported and edited, using .gimp 2.8, and I press in new material, go to new texture, and then after that I assign that vertex group in the UV map to that material, I go into the UV map window and click open image, nothing comes up, then when I click on the render image, it is blank.
It worked with a cube yesterday, but my character doesn’t work with it.
If anyone could help me out I would really appreciate