It's the tale of how Hiccup Horrendous Haddock III, a young Viking from the island of Berk, befriends a Night Fury dragon named Toothless and learns that dragons aren't as scary as he thought.
Hiccup is a small and skinny Viking, not exactly what you'd expect from a Viking. He's not strong or brave, and he's not very good at fighting. But he's smart and curious, and he loves dragons.
One day, Hiccup finds a Night Fury dragon that has been shot down. The dragon is injured and scared, and Hiccup takes pity on it. He names the dragon Toothless, and they quickly become friends.
With Toothless, Hiccup learns that dragons aren't the monsters that everyone thinks they are. They're actually gentle creatures that just want to be left alone. Hiccup also learns that he's not as weak or useless as he thought he was. He's actually a pretty good friend to a dragon.
Together, Hiccup and Toothless go on many adventures. They learn to fly together, they fight off dragons, and they even save the day a few times. And through it all, they learn that friendship is the most important thing in the world.