If the archive contains a mod, it is often best to import it directly through a tool like the Mass Effect Modder (MEM) or the ME3Tweaks Mod Manager rather than extracting it manually.
Because Windows and macOS do not natively support the RAR format, you will need a third-party utility:
Use WinRAR (official developer) or 7-Zip (open-source).
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.