Ensure every file in the set is in the same directory.
Right-click B8.part1.rar and select "Extract Here" or "Extract to [Folder Name]".
You cannot open this file by itself; it is only one piece of a larger puzzle.
To extract the contents, you must have all subsequent parts (e.g., B8.part2.rar , B8.part3.rar ) in the same folder.