You cannot open Part 1 alone. You must have (e.g., part01.rar , part02.rar , part03.rar ) in the same folder on your computer.
Usually, files like this are for games , high-resolution video collections , or software installers . Once extracted, look for an .exe (Windows) or .dmg (Mac) file to proceed.
If any part is missing or has a slightly different name, the extraction will fail. You need software capable of handling .rar files.