Use a tool like WinRAR or 7-Zip to extract the .rar file to a folder.
If you are actually looking for the Destiny 2 weapon guide, these videos show the exact steps to get it and its catalyst:
You must complete the Grasp of Avarice dungeon to earn the weapon.
If you are looking for information on the weapon in Destiny 2 , that is an official in-game item and not related to a .rar file download. Quest: Pick up the "And Out Fly the Wolves" quest from Xur .
If the game fails to launch, right-click the game executable ( .exe ) and select Run as Administrator .