Plot Overview
The Main Plot of the vampire diaries is introduced and told by by one of the main characters, a 150 year old vampire named Stefan Salvatore. His opening line is as follows:
For over a century, I have lived in secret; hiding in the shadows, alone in the world. Until now. I am a vampire. And this is my story.
Stefan Salvatore
Later in the show we learn that stefan has come back to his home in mystic Falls Virginia to meet another one of the shows main characters, elena Gilbert. We discover that Elena looks exactly like someone stefan and his brother damon once knew as a vampire in the 1800s. This is the first of many mysterious occourances in mystic falls.
Pilot Episode first scene
Important Plot Points

Vampires exist!
Vampires exist and they must drink blood to stay alive. Although some vampires only eat animals, most get by on humans, but they don’t have to kill them to feed. Vampires have many powers in the show like super strength, speed, and mind control. Their blood can also heal anyone that is injured; however, dying with vampire blood in your body turns you into a vampire!

Witches…
Behind all the supernatural occurrences and creatures are witches. arguably the most powerful beings on the show, witches are born into magic families and often gone to when someone needs a little help or protection from the supernatural. Their powers have few limits and they can stop most anyone in their tracks with a quick glance.

Warewolves?
Yes, the natural sworn enemy to vampires makes an apperance in the show, but not always as vilains towards the vampires. Warewolves can only be created if someone born into a warewolf gene family triggers the warewolf curse by taking a human life.