Here's out it works: You set the goal and create a Campaign. Then you market the heck out of it, raising as much of your goal as possible. If you if don't reach your goal, you can choose to take what you have raised or refund the money. Either way the choice is yours. There is a small fee at the end of the campaign if you do decide to take money. Not bad for reaching your dreams.
To learn more: http://www.indiegogo.com/learn/why