CPU consists of three basic units: control unit, Arithmetic Logical Unit (ALU) and memory unit.
Input is given through the input devices to CPU.
Control unit controls communication within ALU and memory unit.
Decides which circuit is to be activated.
For reading instruction it uses Fetch-execute mechanism.
Control unit gets instruction from memory.
Control unit decides what to do of that instruction and transfers it to the ALU.
ALU performs various arithmetic operations like addition, subtraction, multiplication, division and logical operations like AND, OR, NOT, NAND etc. on that instruction.
Results of ALU are stored in the memory or resistor for its further operations.
After completing the instruction, stored results are passed to the output devices.
To synchronize all these operations CPU uses its own system clock.