: You only ever need to right-click and extract Part 1 . The software (like WinRAR or 7-Zip) will automatically find Part 2 and stitch them back together.
: Ensure you have part1.rar and part2.rar in the same folder. 2.part2.rar
If you were looking for a literal story related to the "RAR" acronym, here is a recommendation and a quick guide on how these files work: The "Amon's Adventure" Story : You only ever need to right-click and extract Part 1