I made this little alien guy thanks to the Blender cookie tutorials and i got the point were i needed to mark the seams and then unwrap. but when i unwrap the layers are overlapping 
Does anyone know how to fix it ?
Depending on what kind of overlap you are getting, there may be a 1000 things wrong with your seams.
try:
1.Ctrl+P to pack the islands
2.Unmarking some seams
3.Seperating some parts that pose problems
4.Stitching, pinning etc of problematic parts
5.Moving uv vertices around by hand
if you don’t get anywhere with that, you could post an image or blendfile here, so we can actually see whats wrong.
edit: oh, i just noticed you already had an image attached. wasn’t showing for me. it might be a simple matter of pressing ctrl+p (or after that seperating some additional parts)
I can’t see the image, but one common problem is that the normals need to be recalculated ( select all vertexes and ctrl N ) . If some are pointing inward, and some outward, the unwrap will come out weird. another common problem, is that there is no seam somewhere where there needs to be one. this will come out looking all twisted and overlapping on itself.
ok i added an image
