T-54 in Woodland and Desert Camo
Inside each archive you will find multiple files. These include variations of the custom skin, as well as images of the various skin options. The default skins contains the name of the tank followed by .dds (example: T30.dds) and is usually in woodland cmo if there are multiple options. To change to another skin, first rename the default (T30.dds) to something else, like T30_bu.dds, then rename the skin you want to the default (T30.dds).
Download is designed to use the Curse client for installation, or you can unarchive into the res_mods/0.8.x/vehicles/<country>/<tank> folder as appropriate.