Blanche is destitute. She moves into a little apartment with her sister and brother-in-law and, like most guests, becomes a nuisance after a few days. Stanley dislikes her because she interferes with his life with Stella, and Blanche dislikes him because he is a threat to her. She has nowhere else to go. She tries to undermine the close relationship between Stella and Stanley by making Stella see Stanley as belonging to a class that is beneath them. To make matters worse, Stella is expecting a baby, and there is obviously no place to keep a baby as long as Blanche is taking up so much space. Blanche monopolizes the bathroom. She must inhibit the love-making that is still going on between Stella and Stanley in spite of Stella's pregnancy. Blanche uses sweetness and gentility in her conflict with Stanley, while he uses brutality and confrontation. Blanche is the protagonist, Stanley is the antagonist, and Stella is the "MacGuffin" or "bone of contention." Blanche really only has one hope, which is to get married. When this hope fails, she cracks up.
There seem to be many different conflicts between these two central characters, and certainly if we consider Blanche the protagonist of this play, then Stanley is most definitely the antagonist. One of the principal points of conflict between the two of them is the way that they could be viewed as standing for types. Blanche represents fantasy and Stanley the forces of reality that come into conflict with each other during the course of the play.
From the start, Blanche is shown to lie and manipulate the truth. She is quite open with explaining to Mitch that she does this as a way of resisting fate and its power over her. Lying is therefore a strategy that helps her to believe her version of how she would like her life to be rather than the rather depressing reality. Stanley, however, is clearly described as a pragmatic individual who is grounded in reality and the truth. He immediately smells a rat with Blanche's elaborate stories and does all he can to expose them as nothign more than lies. The two characters therefore represent fantasy and fact, or appearance and reality, and this is the conflict that drives the play. The conflict of course is terminated with the way in which Blanche's schemes to free (as she sees it) her sister from Stanley's power and to remake her own life fail.