What is the role of CPU within the computer?

The CPU, or Central Processing Unit performs the calculations and logic functions of the computer. CPU's only perform the most basic of functions, such as adding the contents of a memory location to the contents of a CPU "register", or comparing the contents of one register to the contents of another register and "jump" on a specified condition such as "equal to", "greater than" or "less than". CPU's are also able to initiate transfer of large blocks of data, read or write data to/from peripheral devices, and in general, watch over system functions. Of course, this is an oversimplification of the power and function of the CPU, but it gives you an idea of what is going on. CPU's have the capacity to perform many low level functions that are enhanced when added together into an application. If done correctly, the entire process is transparent to the user and all you see is a well designed application. The heatsink and the cpu needs a fan to cool them off