The guys at PCApex are starting a series of articles that will cover the basics for everything PC-related, & in this first installment, they're covering how heatsiniks work, & exactly what TIM does. A quick read that will answer any questions you may have...

"This is a very very general example of what your CPU cooler does. It takes the heat (molecular vibrations) generated by your PC's CPU and disperses it in order to keep the CPU cool and prevent any heat build up which could kill your processor."