How would I start an introduction to a paper?I'm having trouble on starting an introduction on an essay where I have to compare and contrast Tom...

I think that the best starting point for such an essay is
to simply discuss both characters.  From the most broad points of view in your
introduction, you have a great topic with which to "hook" the reader.  Gatsby and Tom
are linked to the same woman, but represent the different extremes to which men, and all
people in fact, can go.  Tom is a boor, truly devious and self serving.  Gatsby is a
decent man who loves his dreams and their pursuit.  While the former might be
"legitimate" in his business interests and the latter is probably not, the reality is
that the first is incapable of any real love or affection while the second has nothing
but.  I think that being able to suggest in the introduction that these two characters
are the dominant male figures in the novel and between them, Nick, and the reader, have
to assess both could make for a powerful opening to a compare and contrast
essay.