[PAR35]

what the World Bank does

In short, it funnels taxpayer money to third world countries which don't want to compromise their anti-American standing by taking it from the US government directly. The money can either be called a 'loan', or they can be honest about it and call it a grant.

[Sleeping Beauty]

Part two of the question is the most important:

....and why it [the World Bank] is so important to our US economy and US-based multinational corporations?

It helps to read the article and think about why there are so many Wolfowitz "camps" in the White House.

And, here's a secret-decoder clue:

Wolfowitz wanted to clean up corruption in the government of the borrowing nations (not at the World Bank, BTW). Why is it in the World Bank's interest that those borrowing nations have corrupt governments?