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). Mass-Effect.rar
Depending on where the file was sourced, it generally contains one of the following: Because Windows and macOS do not natively support
The file is a compressed archive typically containing assets, mods, or installation files related to the Mass Effect science-fiction role-playing game series developed by BioWare. Typical Contents Mass-Effect.rar
Right-click the file and select "Extract Here" or "Extract to folder".