How do Jem and Scout meet Dill, and how does Scout describe the boy in Lee's To Kill a Mockingbird?

Jem and Scout meet Dill when he comes in the summer to his Aunt Rachel's house to stay with her next door to the Finches.'

One morning, as Jem and Scout go out to the backyard to play, they hear something in Miss Rachel Haverford's collard patch. When they look over the wire fence, they notice a small boy sitting in the yard, but they wait for him to speak. He says hello and introduces himself as Charles Baker Harris, boasting that he can read.

Jem replies that his name is larger than he is, and, as for his ability to read, Scout has been reading "ever since she was born." Dill inserts that he has mentioned his ability in case they wanted anything read.

As they continue to converse, Jem teasingly asks him if he is four-and-a-half years old. Dill replies, "'Goin' on seven." Then Jem comments that he looks puny for that age. Dill asserts, "I'm little, but I'm old." Jem asks Dill how he came to have the name Charles Baker Harris. "Lord, what a name!" he adds. Dill retorts that his name is no funnier than Jem's: Jeremy Atticus Finch.

Despite his teasing, Jem invites Dill to come over to their yard. Jem and Scout learn that Dill is from Meridian, Mississippi, but his mother is originally from Maycomb County. Dill is very articulate as he tells the Finch children about his having won a Beautiful Child contest and his using the money to go to the picture shows twenty times.

Scout describes Dill as an oddity in looks and in how he is dressed:

Dill was a curiosity. He wore blue linen shorts that buttoned to his shirt, his hair was snow white and stuck to his head like duckfluff; he was a year my senior, but I towered over him....[As he talks] his blue eyes would lighten and darken; his laugh was sudden and happy; he habitually pulled at a cowlick in the center of his forehead.

Jem accepts Dill and all three plan how they will spend their summer: They will repair the tree house and run through a repertoire of dramas based upon books they have read.
Finally, after they have exhausted all sources of drama, Dill suggests that they investigate the Radley House and its occupants, as it fascinates him.