Since .rar is a compressed format, you must extract the files before they can be used:
Some packs include specialized scripts or item definitions for modding projects, such as the Moondust Project .
Most packs require you to move the extracted files into a specific directory, such as a game's \cfg\ or \mods\ folder.
Use a utility like 7-Zip or WinRAR to right-click the file and select "Extract Here".