The narrator (the brother) is ashamed to have a brother like Doodle that wouldn't be able to do all the things that a "normal" person could.
The brother (the narrator) is teaching doodle how to walk because he was ashamed to have a brother that couldn't walk.
A storm came in when the brother (the narrator) and Doodle were drifting down the creek. Doodle and his brother were running home trying to get away from the storm. Doodle was trying to catch up to his brother but his brother was mad at him saying he failed.
When the brother (the narrator) finds Doodle dead underneath the red nightshade bush