Planet of Slums

Having just finished reading "Planet of Slums", I can't help but be both depressed and grateful at the same time. Some of the facts in the book made me sick to my stomach, ashamed to be living in a world where things like this are allowed to happen, and made me see that the little inconveniences that I complain about are incomparable to what the rest of the world lives and breathes on a daily basis. There was one thing that was unclear upon finishing that hopefully someone can clarify for me: How do the IMF and World Bank work and what exactly is a Structural Adjustment Plan? It is clear that Davis feels both of the orgs have negatively impacts slums throughout the Third World despite their apparent roles as helpers, but I just don't understand how they function and what they have done. In lamence economics terms please, if possible. Thanks!