A central processing unit (CPU) is the electronic circuitry within a computer that carries out the instructions of a computer program by performing the basic arithmetic, logical, control and input/output (I/O) operations specified by the instructions. 
Below we see a simplified diagram describing the overall architecture of a CPU. You must be able to outline the architecture of the central processing unit (CPU) and the functions of the arithmetic logic unit (ALU) and the control unit (CU) and the registers within the CPU.
Please know and understand:
Memory holds both data and instructions
The arithmetic/logic gate unit is capable of performing arithmetic and logic operations on data
A processor register is a quickly accessible location available to a digital processor's central processing unit (CPU). Registers usually consist of a small amount of fast storage, although some registers have specific hardware functions, and may be read-only or write-only
The control unit controls the flow of data within the CPU - (which is the Fetch-Execute cycle)