In the classic fantasy novel The Hobbit by J.R.R. Tolkien, Bilbo Baggins (the hobbit) accompanies a band of 13 dwarves to the Lonely Mountain, their ancestral homeland, to recover their kingdom and its treasure from Smaug the dragon. Gandalf the wizard is responsible for bringing Bilbo and the dwarves together. He sees something special in Bilbo that he believes will make Bilbo a valuable companion on the quest to recover the treasure. Gandalf knows that Bilbo longs for adventure, even though during their initial conversation, Bilbo isn't even aware of it himself.

When Gandalf and Bilbo have finished talking, Bilbo goes inside in a huff, and Gandalf scratches "a queer sign on the hobbit's beautiful green front door." It is this sign that brings the dwarves together to Bilbo's home. After the dwarves have feasted on Bilbo's food and then cleaned up, Gandalf explains more clearly why he has had the dwarves assemble in Bilbo's home.

You asked me to find the fourteenth man for your expedition, and I chose Mr. Baggins. . . .If I say he is a Burglar, a Burglar he is, or will be when the time comes. There is a lot more in him than you guess, and a lot more than he has any idea of himself.

That's how Bilbo ends up meeting the dwarves and joining them on their many adventures.

Gandalf brings the dwarfs to Bilbo because he wants Biblo to join them on the treasure hunt.  As a wizard, Gandalf knows that Bilbo is not an ordinary Hobbit.  He tells the dwarfs that Biblo is a burglar, even though Bilbo has done no such thing.  Gandalf knows that Bilbo has a special part to play in the adventure.

As it turns out, Bilbo does take to adventuring rather well.  He is scared at first, but when he is captured by the trolls he tells them that he is a burglar, then changes him mind and tells them that he is a hobbit.  They think he is a burra-hobbit.  Gandalf rescues him by tricking the trolls into arguing until daybreak, when they turn to stone.  This is the first time Bilbo realizes that he can be brave.