For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
For a story that fits the "three act plot analysis," look no further than the title story of the book.
Act I
Mr. Kapasi thinks Mr. and Mrs. Das are typical American tourists in Indian bodies. Mrs. Das especially just seems kind of arrogant and aloof. That is, until he mentions that he's an interpreter, not just a tour guide. From that point on (or at least, until the end of the story), Mrs. Das is hooked on Mr. Kapasi's "romantic" job and Mr. Kapasi is totally hooked on Mrs. Das (and her legs).
In fact, he's so hooked on her that he's figured out a way to extend the Das family's trip with him as their tour guide.
Act II
Now that Mr. Kapasi has Mrs. Das interested in him (or so he thinks), he's happy. But wait—Mrs. Das ends up telling him all about her nasty little secrets (like the fact that Bobby isn't Mr. Das's son), which totally crushes Mr. Kapasi.
In fact, he's so disappointed that he makes one of those no-turning-back comments: he suggests to Mrs. Das that her physical pain is because she feels guilty about her affair and Bobby's secret father. There's no way Mrs. Das can forgive that comment, so she leaves the car.
Act III
Everything that happens after Mrs. Das walks out of Mr. Kapasi's car is like a series of bad coincidences that highlight how truly selfish Mrs. Das can be. The ending shows how there's no way Mr. Kapasi will ever be able to view Mrs. Das—or the entire Das family—favorably.
It's a pretty subtle resolution, but at least you know for sure that Mr. Kapasi's totally over his temporary infatuation and has come back to earth hard.