Use the Refurbished Demolisher to destroy 150 Decomposed Ghouls, 20 Frostskull Mages and 2 Bone Giants in the Valley of Lost Hope. Speak to Matthias Lehner at the First Legion Forward Camp when you've completed this task.
You're going to use this machine against the Scourge? You're not going to win against them like that.
You can destroy hundreds... even thousands of them. But you won't win. Not out here.
When you're done playing with your machine, meet me to the north. There is an old army encampment. What I will show you will teach you a little bit about who you're up against.