I want to write a paper about the vampire in Dracula, but I don't know were to start and I need an argument.

With a complex and brilliant novel like Dracula, there is no shortage of paper topics you could choose. In regards to the novel's titular character, Count Dracula, you could make a quite strong paper by suggesting him to be a symbol of sexuality. 
Written in 1897, Dracula tackles the sexual mores and standards at the tail end of the Victorian era. The idea of being sexually open, even at the turn of the century, was a socially preposterous one. Count Dracula himself acts as a symbol of open sexuality through the metaphorical hunger for new and fresh blood. The Count, as with the other vampires in the novel, feed on the sharing and consumption of bodily fluids, as well as the penetration of flesh through the blood-sucking fangs.
One of the novel's important characters, Johnanthan, feels overpowered and emasculated by the suave and machismo Count. Dracula acts as a symbol of the human sexual desire, luring young innocent women to their "moral doom" by making them like him: blood-thirsty, flesh-craving creatures of the night.
With Dracula being one of the earliest tales of vampires and the nosferatu, it is no surprise that in recent times vampires have been sensualized in novels like Twilight. Bram Stoker had been doing the same work, only well over a century earlier!
https://www.biography.com/writer/bram-stoker