What does constructivist theorist A. Wendt mean with his article "Anarchy is What States Make of it"?

This is a long article that is one of the seminal works of
theory in the field of International Relations.  A full summary is impossible in the
space available here.  What I can give is a very basic summary of Wendt's major
point.

In this article, Wendt is taking issue with the main
claim that realists make -- that states are forced to act in certain ways because the
international system is anarchical.  Realists claim that anarchy, by necessity, causes
states to come into conflict with one another.

Wendt takes
issue with this.  He argues that there is nothing in anarchy that makes conflict
necessary.  Instead, he says, states' actions towards one another are based on their
attitudes towards themselves and toward other states.  In other words, Wendt is saying
that a state develops its own identity and it gives identities to other states.  It acts
towards other states based on how those identities match
up.

Perhaps you can think of this by means of an example. 
Iran sees itself today as a major Islamic power that should have more influence in its
region.  It sees the US as the major threat to it both as a Muslim country and a
regional power.  Therefore, it acts aggressively towards the US.  By contrast, Saudi
Arabia does not act aggressively toward the US because it has not constructed this image
of the US as a "Great Satan" that hates all Muslims.

So
what Wendt is saying is that states construct visions of themselves and others and act
based on those visions, not on the basis of the fact that the international system is
anarchical.