Seeing as I'm not busy - I will try to explain each part very shortly, as it would relate to the computer if seen as a human body.
CPU: This is the brain of the computer. This is where all the thinking happens.
RAM: This is short term-memory. It acts as a fast bridge between all the other parts and the CPU. It helps to overcome speed difference between devices.
Hard Drive: Long term memory. This is where information is stored for long-term permanent storage.
GPU: You could think of this as the "mouth" of the pc. This is the part that allows the computer to show you whats happening. It allows the system to graphically communicate with you.
Motherboard: The backbone of the system. This is what connects all the parts together, so that they can work together and communicate with each other.
PSU: The stomach. Hehe. This is where the system gets its energy from.
Network Card: This would be your computer's phone. It allows your computer to connect and talk to other computers.
Without these basic components, a computer would not function. (Rare exceptions for drive-less systems, but lets not split hairs.)
Other components to a computer serve additional purposes. Mostly these purposes are to ease our own communication inputs and outputs with the computer.