Many community-created mods for the original trilogy or the Legendary Edition are distributed in .rar format. These often include .pcc (meshes/textures), .afc (audio), or .sfar (DLC) files.
Depending on where the file was sourced, it generally contains one of the following: Mass-Effect.rar
Use WinRAR (official developer) or 7-Zip (open-source). Many community-created mods for the original trilogy or
Right-click the file and select "Extract Here" or "Extract to folder". Mass-Effect.rar