In this story, Bradbury does not explain in any detail what has happened to the city of Allendale. Instead, he gives descriptive clues to make the reader aware that there has been a nuclear blast in the city. This house is one of the few survivors of the blast. Outside, the blast is evident all around: one side of the house is "charred," for example, and there are charred silhouettes of some of the victims. Another survivor, the family dog, is covered with sores caused, presumably, by radiation sickness.
By not explicitly describing what has occurred in Allendale, Bradbury is able to focus on his central message: that we must not rely too heavily on technology, because technology is capable of considerable destruction. Bradbury really emphasizes this point in the closing lines of the story, in which the reader is left with the image of a ruined, burned-out house. The only survivor is a talking wall, a symbol of man's over-reliance on technology and his desire for convenience.