I see from your tags that your focus for this essay is symbolism. Indeed, Hemingway's "Hills like White Elephants," is rich in symbolism. First of all, you need a thesis statement. Once you have decided on a thesis, the rest of your outline becomes much easier to complete. Your thesis might be something like the following:
Hemingway's symbolism in "Hills like White Elehants" not only reveals the subject of the couple's discussion, but also the choice that they ultimately make.
With a thesis such as this one, you can complete your outline. The following is only a suggestion:
I. The title as symbol
A. "White Elephants" symbolizes change in relationship (Look when the girl first mentions the "white elephants.")
B. "White Elephants" refers to the unwanted baby (A "white elephant" sale is one in which people get rid of their unwanted junk.)
II. Setting as symbol
A. Railroad, situated between a dry valley on one side and a fertile one on the other symbolizes choice
B. Unshaded, dry land symbolizes death
C. Fertile land symbolizes life and fertility
And you can go on from here with other symbols such as the couple's luggage that symbolizes their past and the Anis del Toro--the drink that the girl orders, whose bitter taste may symbolize the change in their relationship.