Most good stories start with a fundamental list of ingredients: the initial situation, conflict, complication, climax, suspense, denouement, and conclusion. Great writers sometimes shake up the recipe and add some spice.
Exposition
Make Love Not War
Troilus wants to hook up with Cressida, not fight in some dumb war that's been dragging on for the last seven years. Problem is, Cressida's been playing hard to get. Meanwhile, the Greeks wish their best warrior (Achilles) would come out of his tent and fight, but Achilles is playing hard to get, too. Basically, in the exposition, Shakespeare sets up and develops two separate plots (a love plot and a war plot). Confused? Don't worry—that's what the rising action is for.
Rising Action
Your Cheatin' (and Dyin') Heart
Cressida is traded to the Greeks and betrays Troilus with a dude named Diomedes. Also, Hector kills Achilles' lover/ bestie, which really irks Achilles. Meanwhile, Troilus battles Diomedes but, uh, nothing really happens. Now we're all ready to see what happens when Achilles storms out of his tent for the big climax.
Climax
Sword It Out
Troilus' battle with Diomedes may have been anti-climactic, but Shakespeare finds a good substitute when Achilles and his gang of Myrmidons mow down Hector. Our hero is slain: definitely a climax.
Falling Action
Remind Us Not to Tick This Guy Off
A guy like Hector deserves some props but Achilles is totally disrespectful when he has the dude's corpse tied to a horse so it can be dragged through the dirt. Now we're seeing the effects of all the upsetting climax: dishonor, dishonor, and more dishonor. We're not exactly expecting a happy resolution.
Resolution
So Long, Troy
Now that their best soldier and military leader is dead, Troy isn't looking so good. Bummer, right? Well, Shakespeare can't just leave well enough alone. In the last lines, Pandarus tells the audience that he hopes we all get an STD and die. Gee. Thanks. Way to wrap it up, guys.