What is the point or purpose of each of the acts in "Romeo and Juliet"?

Look at the parts of a plot
line in a basic short
story:

1. Exposition: background information,
   setting, character introduction, conflict.


2. Rising Action
   (and complications): events leading to the climax of the
   story.


3. Climax: the highest point of action in a
   story.


4. Resolution: the solution to the initial
   problem.

Each of the acts in "Romeo and Juliet"
can be fit into one of these parts.

The prologue in Act 1
presents most of the exposition of the story.  It is brief
but complete.  The characters (though not by name) are introduced, the problem/conflict
of the two families is introduced, and actually, the end of the story is revealed.  The
initial fight scene actually demonstrates the conflict between the two houses.  Finally,
the Prince's decree at the end of this scene is what initiates many future complications
in the story.

Acts two through four and the very beginning
of Act 5 are all parts of the rising action of the play. 
These acts, of course, contain the "meat" of the story which continues to build in
action, emotion, and anticipation of the climax.  Several
complications are introduced as the action progresses,
including Juliet and Romeo falling in love and marrying without consent, the deaths of
Mercutio and Tybalt, and the banishment of Romeo.

The play
ends almost as abruptly as it began, therefore, the climax
and resolution take place in Act 5.  The
deaths of Romeo and then Juliet are the very peak of the action in the story.  As a
result of their deaths, however, the two families realize the errors of their ways and
finally forgive one another, which is the resolution to the original
conflict.