"Part01.rar" acts as the entry point for the entire set.
You cannot usually extract the contents using only Part 01; you must have all parts (01 through the final part) in the same folder for the extraction to succeed. Part01.rar
The file is the first volume of a multi-part split archive, a common format used to break down very large files into smaller, more manageable pieces for easier downloading or sharing. Understanding Multi-Part Archives "Part01