It all starts with many dwarves and Gandalf arriving at Bilbo's house to discuss the problem the dwarves have with their hometown.
Thorin starts by saying that the journey will be tuff and dangerous and they may not be able to make it back alive.
WE CONQUERED HIM!!!
The dwarves have their supply of gems and jewels that they mine in the darkest caves and while they work on the mines they sing of joy and happiness.
So, will you come?
Yes, I will join you for this journey
Then, one day, a huge dragon came and took the dwarves gems and jewels and is keeping them away from them. He's guarding them, with his fire-breathing mouth and scaring them all.
Their whole goal is to defeat the dragon for once and for all, but the problem is that they need help defeating the dragon, Smaug, and then getting back all of their special gems and jewels that they so desire to have.
He ends the story by asking again if Bilbo will join them and help them on this journey to get their precious gems and jewles back from the feirce dragon, Smaug.