Somebody help me,. why i cannot install theme skeleton shop site into my grav Shop-site
A skeleton is a fully working site you can use to start with, not something you install in your own site.
To use it, download the skeleton from the Grav site and copy it in your web root folder.
I need to fix the skeletons page on the downloads to not include the GPM instructions, this is not correct. As Flavio says, you just download the zip and unzip it like a normal Grav install. They contain everything already.