The file could be related to a few different things, and the process for "creating a feature" depends on which one you mean:
: Are you looking to create a specific design feature (like a toolpath or a shape) within a project file that was shared as a .rar? VTcS2.rar
: Is this a source code archive where you want to add a new functional feature to the program? The file could be related to a few
Could you clarify what kind of you are trying to create and what software you are using to open that .rar file? VTcS2.rar
7-Zip / Feature Requests / #1198 Option to create RAR files?