When Harry and Cedric land, Harry's leg gives out. Cedric pulls Harry up and they see that they're in a dark graveyard. Neither of them knew the cup was a Portkey and they discuss whether this is part of the task. Harry feels like someone is watching them and notices a figure walking towards them, carrying what seems like a baby in its arms. When the figure stops, Harry's scar explodes with pain. As he writhes on the ground, he hears Voldemort say, "kill the spare" and then he hears the Killing Curse. Harry vomits from the pain. He opens his eyes to see Cedric, dead beside him.
The language that Voldemort uses to describe Cedric--he's not even human, just a "spare"--shows that Voldemort doesn't value life at all, other than his own. It's also important to note that Cedric dies just because he inadvertently crosses Voldemort's path, not because he did anything wrong. This flings Harry into the adult world, where things don't always happen for good reasons and aren't fair.
Before Harry can process this, the figure, Wormtail, lifts Harry and ties him to the headstone of Tom Riddle’s grave. Wormtail stuffs cloth in Harry's mouth and then walks away, leaving Harry to stare at Cedric's body and the bundle. Harry's scar blazes again. He notices a giant snake circling the headstone and sees Wormtail return with a full cauldron. He lights a fire and when the cauldron's contents are hot, Wormtail opens the bundle. It contains a horrific child-shaped figure that's scaly, red, and snakelike, and Wormtail drops it into the cauldron.
While Voldemort dehumanizes everyone around him, it's telling that the body he currently possesses seems far from human--it's revolting in a way the text's tone suggests is beyond the capacity of the human body. When Harry doesn't have the time to process Cedric's death, it reminds the reader that life moves quickly and, going forward, Harry won't necessarily have time to mourn losses or properly prepare for tragedy.
In a terrified voice, Wormtail draws bone from the grave at Harry's feet and puts it into the cauldron. He pulls a dagger out and Harry closes his eyes so he doesn't see Wormtail cut off his own right hand and toss it in. Then, Wormtail takes blood from Harry's arm and adds it to the mixture. The potion turns a blinding white and Harry hopes that the creature will drown. Thick steam starts to rise and Voldemort emerges from it.
With Voldemort's return, the novel heralds the beginning of something most witches and wizards thought ended thirteen years ago and demonstrates that history can and will repeat itself when individuals in power don't do enough to stop it.