You must download part1.rar , part2.rar , part3.rar , and so on, until the set is complete.
A file named part1.rar cannot be opened or used on its own. It is the first link in a chain. To access the actual content (likely a movie or a high-quality recording of a performance by the band Pantera), you generally need: P4NT3R4HD.part1.rar
Tools like WinRAR , 7-Zip , or The Unarchiver are used to "extract" the data. You must download part1