What is the purpose of using sources in an essay and what is the best way to implement sources in your essay? Finally where can you go for sources and what makes a source credible or non-credible?

Why does pumblechook choke on the brandy at christmas dinner? a. he has had too much to drink. b. mrs. joe had only spoiled brandy to serve him. c. pip replaced it with tar water. d. he becomes overexcited telling his story.