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 (Initial Situation)
We've Created Robots! Yay!
Rossum's Universal Robots is churning out artificial people to do all your dirty work. The prologue tells you about the robots and introduces the main characters, Domin (the jerk in charge of the robot factory) and Helena (the idealist who wants to save the robots and ends up marrying Domin for reasons which are unclear but probably have something to do with the fact that she's the only woman in the play, so she has to marry someone because the play is somewhat sexist like that).
Rising Action (Conflict, Complication)
We've Created Robots! Yay?
Act 1 is set ten years after the prologue. There are hints and threats and then the full-out realization that the robots are revolting and humanity is in danger of complete and utter extinction. Way to go R.U.R, you dopes. (Though, to be fair, if the robots didn't go kerblooey and try to kill everyone, there wouldn't be a whole lot of action in the play now, would there?)
Climax (Crisis, Turning Point)
We've Created Robots! Oh dear.
Right at the end of Act 1, the robots are ready to attack.
Falling Action
Everybody Dies
The end of Act 1 looks like the situation is hopeless for humanity. Act 2 is about assuring you that, yep, it really is hopeless. Everybody on earth dies, including the characters you've grown to know and not really care about that much since they're not very interesting as characters for the most part. But, interesting or not, they're dead. Robots rule. Although, no one knows how to make more robots, so the robots will all die too, given enough time—bummer.
Resolution (Denouement)
Happy Unconvincing Ending
In Act 3, the one man still alive, Alquist, moans a lot about being the one man still alive. Also, two robots—Primus and Helena—discover they have souls, fall in love, and walk off into the sunset. At about the same time, Alquist discovers the secret of making more robots. If it sounds improbable, that's because it is. Be happy, if unconvinced.