"Forward, the Light Brigade! Charge for the guns!" he said. (lines 5-6)
This line tells us pretty much all we need to know about the plot of this poem. The soldiers in the Light Brigade have to "charge for the guns." Sound like a good idea? Probably not, and the Light Brigade knows it. Still, that's what war is all about – doing dangerous things that you normally never would, like riding your horse toward a bunch of cannon. Tennyson throws us right into the middle of this.
Oh, also, notice the "he" up there? We never find out who that is. The guys giving the orders are anonymous and invisible in this poem.
Cannon in front of them Volleyed and thundered; (lines 20-21)
More intense war descriptions. Just imagine what it would be like to hear the rumble of cannon firing at you, sounding just like thunder. Don't forget that these guys aren't in a tank or a Humvee or something. They're on horseback, with nothing to protect them from the whizzing bullets and cannon fire.
Flashed all their sabres bare, Flashed as they turned in air (lines 27-28)
This is a pretty romantic, studly image, isn't it? It makes the soldiers of the Light Brigade sound like medieval knights attacking a castle. We can just see those glittering swords shining through the smoke. Now, as to whether it's a good idea to attack cannon with a sword, we're not sure. That's kind of how it goes with the Light Brigade in this poem. You like them and feel for them and don't want them to die. At the same time though, there's something a little sad and doomed about these guys. The whole thing, the charge, the swords, the horses – it doesn't sound all that well thought-out, does it?