The CPU has helpers that help it do it's job. This performs simple mathematical functions. This handles more complex functions. While the ALU and FPU are doing their jobs, they need somewhere internal to the processor to store data. These places are called registers.
Registers are nothing more than holding places for bits of data.
The CPU also communicates with other devices on the external data bus. If a program requires the CPU to access a device, such as a sound card, then the CPU will send a command to the sound card on the external data bus, and then the sound card will send a response back to the CPU, or perform a function. As the families of microprocessors have evolved, many new elements have been introduced into the microprocessor, such as caching , enhanced instruction sets and clock doubling . These have helped to make processors faster and capable of doing much more work quickly. The various families of processors have also supported different modes of operation.