Consider the beginning of the film The Glass Menagerie. How does it differ from the play? What does this difference in the film add to our understanding of the play?

The Glass Menagerie is a critically acclaimed drama written by famed American playwright Tennessee Williams, first published and produced in 1944. As the main protagonist narrates the events of the play, drawing them from his memory, The Glass Menagerie is classified as a memory play. Williams apparently based the majority of the plot on his own experiences, which is why The Glass Menagerie is often considered an autobiographical play, as well. Because of its extremely positive reviews, the play became one of the most popular dramas in American literature, and Williams was recognized as one of the most influential American playwrights of his time.
When mentioning the eponymous film, I assume you mean the 1987 production, directed by Paul Newman and starring Joanne Woodward and John Malkovich. This is actually the fourth movie adaptation of Williams’s play, following the 1950 feature film directed by Irving Rapper, and the 1966 and 1973 TV films. Unlike the play, the film received positive to mixed reviews; some critics praised it, while others described it as too theatrical and melodramatic.
Both the play and the film focus on Tom Wingfield—the narrator and the main protagonist of the plot, who remembers his past and his family which consists of his mother Amanda and his elder, crippled sister Laura. One of the main differences between Tom in the play and Tom in the movie is the characterization; in the play, Tom is very expressive and doesn’t hide his emotions, in contrast, Tom in the movie is a bit more reserved.
When it comes to the comparison between the beginning of the play and the beginning of the movie, it’s safe to say that there isn’t a big or a significant difference. In fact, there are more similarities than there are differences. Newman kept all of the original dialogues and monologues from the play, almost word for word, including the narrations.
The setting is also the same, both the movie and the play open in the Wingfield’s small apartment in St. Louis, and perhaps the only difference between the two settings is that in the play, we can imagine how tiny and claustrophobic the space might be, while in the movie, we don’t really get that kind of a feeling.
To conclude, the only major difference between the two beginnings, and between play and the movie, in general, seems to be the characters’ portrayal. Other than that, the rest is pretty much the same. However, I must mention that if you want to understand the film better, you should consider reading the play first; I feel that the most important symbols and elements of the play are almost impossible to find in the movie.
Thus, the play might offer more dimension to the characters, especially the main ones, in comparison to the movie, which might help us understand and empathize with them better. Nonetheless, Newman's film remains to be the most accurate and authentic visual representation of Williams's play so far.