"The Scarlet Ibis" is the story of two brothers, one, the narrator, called Brother, and the younger of the two, Doodle. Doodle is born a very sickly child, whom no one expects to live, and whom Brother feels a tremendous amount of, for lack of a better word, shame.  Brother wanted someone who could run and jump and play with him; instead he got the fragile Doodle.  Determined to make him into the brother that he wants, Brother pushes him constantly past the point of physical endurance; he is often cruel to him, even making him touch the coffin that was originally built for him as a baby.  Doodle does learn a lot from Brother, but everything he learns comes at a very high and dangerous price to Doodle in the end.

Here's a link to a good brief summary on Wikipedia

Brother is the lead protagonist of the story and also the narrator. He is not given a name but is referred to by Doodle, his brother, only as "Brother." He is six years old when Doodle is born. Brother has a high opinion of his own ability to run, jump, and climb, and wants a brother with whom he can share these activities. When it becomes clear that Doodle is capable of little more than lying on a rubber sheet and crawling backwards, Brother grows ashamed of Doodle's limitations and regularly taunts him. Though Brother loves Doodle, the love is tainted with cruelty and embarrassment.

Doodle is the mentally and physically retarded younger brother of the narrator, Brother. His family initially calls him by his given name, William Armstrong, but Brother nicknames him Doodle. Doodle's real strengths lie not on the level of his physical prowess, but on a more subtle inward level, to which Brother seems blind at the time the action takes place. From the beginning of his life, Doodle defies death and refuses to recognize the coffin that Daddy builds for him as his own. He shows a sense of wonder and respect for the natural world, crying with wonder at the wild beauty of Old Woman Swamp.

The other characters are Daddy, Mama and Aunt Nicey.

"The Scarlet Ibis" presumably takes place in North Carolina (the home of author James Hurst, and the setting of many of his stories) just prior to 1920. The narrator, only identified as Brother, reminisces about his younger brother, Doodle, who is both mentally and physically disabled. Doodle was a tiny baby who was not expected to live long, but his inner strength and determination led him to accomplish many things that his family could never have imagined. Brother secretly teaches Doodle to walk, revealing his new talent on his sixth birthday, much to the amazement of the family. Through Brother's tutelage, Doodle manages to enjoy many of the pursuits of a normal boy--swimming, climbing trees and daydreaming about his future. During the summer of 1918, a scarlet ibis--a bird not indigenous to the Carolinas--is found roosting in a tree following a hurricane. The bird drops dead from the tree, and Doodle buries him. The bird serves as a symbol of ill fortune and death, and later that day, the brothers head out for an afternoon of rowing on Horse-Head Landing. The strenuous workout is too much for little Doodle, who falls in the mud and becomes frightened by the lightning storm that is approaching. Disappointed that Doodle has not been able to succeed at all of their physical endeavors, Brother leaves Doodle behind. Despite Doodle's cries for help, Brother ignores him; when Doodle does not return, Brother goes back for him and finds him dead, bleeding from the mouth that has stained his shirt a crimson red. Brother recognizes the similiarities between his dead brother and the dead bird--both weak, blood-stained, and out-of-place in their little world.