Robert Reich has an article plus a video demonstrating how Romney made his money at Bain capital. Reich is Professor of Public Policy at the Goldman School of Public Policy, part of the University of California. Reich served under three administrations Ford, Carter and Clinton.
Romney borrows money and uses it to buy a majority stake in a company. After taking over the board he votes his company Bain a large management fee. He borrows from the company's bank to pay back those who loaned him money. The money also pays bonuses for Bain managers.
The Bain managers cut the number of employees, benefits, and much else to help pay back the bank loan. For much more see this article and the appended video.