For a comparison essay on two pieces of literature, you'll want to compare the literary elements and the literary techniques. Literary elements are things that all narratives (literature) have in common. All have things like a point of view (is a character talking for themselves or is someone else talking for them?), narrator (who is telling the story), chronology (the time sequence of events), tone (the emotion the narrator feels for the characters and events) and mood (the emotional atmosphere within the characters and events themselves). Literary techniques are things that authors choose to include that may be the same as or different from what other authors choose. Techniques include things like symbolism, metaphor and simile, imagery and irony.
To start your comparison between "Hills Like White Elephants" and "Two Kinds" you can analyze the element of point of view. In Hemingway's, someone is telling the story about the two characters. This is a third-person narrator speaking about the story as it happens to someone else, not to the narrator. In Tan's, the main character is speaking for herself and telling her own story. This is a first-person narrator speaking about her own story.
Then you can analyze the element of narrators. In Tan's, the first-person narrator is emotionally involved with the story and uses descriptive words to tell about her feelings and her mother's feelings ("I performed listlessly ... I got so bored"). In Hemingway's, the third-person narrator is distanced and not involved. This narrator avoids descriptive words and lets the characters express their emotions through the content of their speech ("The man called 'Listen' ...").
Continue analysing other elements in this same way and finding what is the same and what is different in things like chronology, tone and mood: the narrator's tone about the story may be different from or the same as the mood; example: the mood of the story might be frightened and scary but the tone of the narrator might be bored or irritated. Then look for techniques to analyze, like symbolism.
You can analyze the technique of symbolism. In Tan's, she is telling a straightforward true story from her own life as a result, there is not much, if any symbolism. [Symbolism is one thing represented by another thing (e.g., a cold stone symbolizing someone's lack of love).] In Hemingway's, the narrator does provide some symbolic representation in the title and descriptions given. The "white elephants" are a rare and revered type of elephant that few are privileged to see ("No, you wouldn't have") and symbolize the pregnancy choices being covertly discussed. The description of the valley and dry land symbolizes the choices before the couple ... and the two individuals. This should get you started on your comparison. Continue to look for and analyze other techniques these authors might have used.