The second wish was Mrs. White's wish that her son, Herbert, would come back to life.
In this story, Sergeant-Major Morris comes to the Whites' house and shows them the monkey's paw. He tells them about how there is the curse on it. They don't really believe that it could cause as many problems as Morris says it does so they take it.
They first wish for 200 pounds (money). Instead of just getting it as a prize or something, they get it as compensation when Herbert is killed at work. After that, Mrs. White makes the second wish -- for Herbert to come back to life.
In the story "A Monkey's Paw" the reader is introduced to the idea of the paw having three wishes available. The White's are excited that it may actually have the powers but they are in doubt. They make a wish for money, but their beloved only son is killed. They gain money through an insurance settlement due to his death.
Mrs. White is devastated. She does not think about what her son would look like or how he will behave. She is crazed with the need to bhaving him back alive. She wishes for him to live. He returns and bangs on the door. The realization that he will be in a horrid state dawns on her husband.
This leads to the last wish. The monkey paw has proved to be evil.