Hi,
I'm not sure if I have time to write a full tutorial. I also find it difficult to find the right words sometimes to explain things. LOL! For more info on Pepakura, your best bet is to visit the 405th Halo costuming forum. There are loads of tutorials there, that explain all you need to know.
Also, if I did list the products I use here, you may not be able to get them in France? For example, "Bondo" is a US brand that we don't get here in the UK. Though any polyester based car body filler is suitable.