The following is taken from Kickstarter's info page.
Every project creator sets their project's funding goal and deadline. If people like the project, they can pledge money to make it happen. If the project succeeds in reaching its funding goal, all backers' credit cards are charged when time expires. If the project falls short, no one is charged. Funding on Kickstarter is all-or-nothing.
Backing a project is more than just giving someone money, it's supporting their dream to create something that they want to see exist in the world.