Most good stories start with a fundamental list of ingredients: the initial situation, conflict, complication, climax, suspense, denouement, and conclusion. Great writers sometimes shake up the recipe and add some spice.
Exposition
Boy Meets Planet
Kelvin, our somewhat uninspiring hero, goes to Solaris station and finds everything higgledy-piggledy: Gibarian dead, Sartorius locked in his room, Snow snowing unpleasantly, and an inexplicable semi-nude black woman wandering around. That's the initial mucked up situation that Kelvin has to navigate. We're not sure of much, but we're also definitely not in Kansas anymore.
Rising Action
Boy Meets Alien Construct of Girl
Kelvin is visited by an alien reproduction of his dead ex-wife, and then by another after he kills the first. He is freaked out at first, but then falls in love with her. Kelvin's relationship with Rheya is the main emotional conflict and complication of the story; they're the two characters you know most about, and really the only ones who have any meaningful extended interaction. They're the ones who matter, and what happens to them is what you're going to care about, if you care about anything, which this book doesn't exactly insist you do.
Climax
Boy Meets Brainwave
Solaris is one of those books where not much happens, and what does happens slowly. The rising action doesn't so much rise as drift, with Kelvin cogitating and reading and then doing nothing some more.
Given that, it's somewhat hard to figure out a climax or a crisis. But if Shmoop had to find one point, Shmoop guesses Shmoop would choose the moment where Kelvin allows Snow and Sartorius to read his EEG.
It doesn't feel like a big deal, but it's when the scientists get what they need to stop the visitors from coming back. Kelvin's vision of his father and Giese (11.25) also suggests this is an important turning point. Kelvin even more or less says the rising action is done: When Sartorius asks, "Do you think that stage has been successful, Dr. Kelvin?" Kelvin says, succinctly, "Yes" (11.28-29). It's not much, but then again, anticlimax is kind of what Solaris is all about.
Falling Action
Boy Meets Grief
The scientists have the key, and now it's only a matter of time until Rheya kills herself. The resurrection is over, so now it's time to get back to death. Action here passes almost entirely out of Kelvin's hands; he does even less than usual as the scientists and Rheya and even the ocean (with its weird storming) conspire to get things back to normal. Not only is the action falling, but Kelvin seems to have fallen out of action altogether.
Resolution
Boy Meets Planet, Slight Return
Just like the rising action didn't really rise and the climax didn't really climax, the resolution doesn't resolve much. Kelvin goes out to see the ocean for himself, and decides to wait for Rheya's return, which is more or less what he's been doing the whole time. He's living with his grief—but he's always been living with his grief, and he'll go on living with his grief. And so the story ends.