Installation
It is a Java program so you must have Java installed. The latest version of Java is still working.
The PWCG download is a zip file. Download it to your BoX installation directory. Unzip the file to your BoX installation directory. PWCG will install itself in a folder called PWCGCampaign. Practice the same for the PWCG archive for Flying Circus.
Skin Pack :
Many skin packs are available for a large amount of data.
Here's a recap of the downloadable skin packs by aircraft type:
These skins will then be copied into the corresponding directories of your Il Great battle installation (for example: C: \ Program Files (x86) \ 1C Game Studios \ IL-2 Sturmovik Great Battles \ data \ graphics \ skins) to be used by PWCG.
Each of your future cooperative mission users will have to copy the skins they want to use on their own PCs.