It's easy to imagine our speaker sitting at a bar shooting the breeze with his buddy, trying to make him understand what it's like to shoot a man face to face on the battlefield. That's the easy part of the setting.
What's trickier is understanding the historical context in which it was written—which can tell us a great deal about what's really going on here. Like many of Hardy's famous poems, this one was written in the aftermath of the Boer Wars, which was waged between the Brits and the locals in South Africa, which they colonized. It was a brutal, messy war and it cost a lot of lives. So we can see where Hardy's coming from in dramatizing this one soldier's response.
Hardy was a realist through and through, and he was part of a growing movement in literature that believed in telling it like it is. You'll notice that we don't really get an opinion on the war in here—or about war in general. Hardy wasn't trying to tell us he was in favor or against the Boer Wars. In fact, he wasn't even trying to tell us whether he's in favor or against war in general. Instead, he's telling us that no matter our opinions, war is the pits.