Explain the diffrance between plot and theme

Read the excerpt from flannery o'connor's "the life you save may be your own although the old woman lived in this desolate spot with only her daughter and she had never seen mr. shiftlet before, she could tell, even from a distance, that he was a tramp and no one to be afraid of. his left coat sleeve was folded up to show there was only half an arm in it and his gaunt figure listed slightly. which phrase connects these characters to the southern gothic genre? half an arm she had never seen his left coat sleeve folded up

Correct sentence. when her brother boarded the ship bound for america, christina stood on the pier and tearfully waved goodbye.

How do i correct this sentence correctly?