The basic plot structure is pretty easy to understand, but I hate to say it: most writers can't/won't/don't follow it as well as they should. There is something to be said for being experimental, but if you analyzed even the most experimental books from Joyce and Woolf, you'd still find the standard narrative plot structure underneath all of their experimentation.
(Now, this is definitely true for novels, but in short stories, you can get away with a little more deviance from the norm.)
As far as just what the basic plot structure is, here's a nice diagram:
The start of the story is the Exposition or Inciting Incident. This is basically the moment where the story begins - narratives, on the other hand, can begin anywhere. It's a rule of movie-making that you begin literally as late in the game as possible, to avoid backstory at all costs. Novelists tend to forget this rule - often to their novel's detriment.
This idea of starting late in the plot comes from an even older idea: in media res, meaning, in the middle of the story. A novel should begin after the plot has begun, or, at the very least, the moment the plot causes conflict for the main character(s). Why? Because you really only need a page or two of Exposition or setting the scene before the reader understands what's going on.
Next up is the Rising Action, essentially a slow build of plot twists, all leading to the Climax. Rising Action is pretty much easy to identify - it's the biggest part of the narrative structure and is basically everything from the beginning of the story until the point when the shit hits the fan. The goal here, for a writer, is literallymaking every scene lead to that Climax - that's the whole point of Rising Action. Each scene must increase the tension and conflict in some way. Otherwise, it doesn't belong in the book, since it's not "rising" the action.
The most important moment in the book is the Climax, which is the moment that decides the entire fate of the plot. The plot's problems are resolved here, the tension that's building in the Rising Action dissipates, and the characters (those that survive, of course) either get pushed towards their happy ending or, at least, their conclusive fates. Normally, the reader can see where everything is going from this point on. The major plot points are finally understood, and the mysteries have been solved.
Some novels end directly following the Climax, leaving little room for the Falling Action and the Resolution (or the Denouement). Others continue on for a while - there could be a flashfoward in time to reveal the characters' fates, or simply a suggestion of what happens to the characters once the reader leaves them. These moments are called the Falling Action and the Resolution, with the Resolution literally being the narrative's final scene.
Essentially, in modern stories, the Falling Action and the Resolution are combined to form probably only a chapter, perhaps less. Readers today have far less patience for a story with a long ending - they want to know what happens and then they want out. If the reader has already seen the plot points resolved, they're going to want the book's resolution to happen within the next 30 pages or so. Otherwise, they're going to get bored.
And that's really why the standard plot narrative structure is the backbone of all stories. Sure, you can play with the order (telling things out of order can be fun, but just remember to avoid backstory), but in the end, the reader needs to be able to still feel the Climax of the book. Without the Climax, the ending will be feel unearned to the reader, and the book's power to emote will be utterly diminished.
So, remember, plot stucture is good. Even when it gets annoying or hard to follow.