Specific Jobs of each PC part

I could write a book about this but I'll try and keep it simple and cover only the basics.

Power supply: This is what keeps your PC running. It converts noisy AC power from the wall into nice smooth DC power for your PC.

RAM: RAM is classified as "primary memory" and can be described as the PC's blackboard or scratchpad. It can be accessed very quickly, it can be erased and overwritten many times, but is expensive and limited in size. The primary purpose of the RAM is to serve as a mechanism for storing and organizing what the PC is working on right now. RAM is also volatile; as soon as the PC loses power, the contents of RAM are lost.

Hard Disk: Hard disks, Optical disks, and removable storage are classified as "mass storage devices" or "secondary memory". If the RAM is described as a blackboard which is easily viewed and accessed, mass storage devices are like encyclopedias. They can hold a heck of a lot more, but take a lot longer to access. Since they take a lot longer to access, they're unsuitable for storing what the PC is working on right now and instead store what the PC has worked on, can work on, or will work on. Whenever data is needed, it is loaded from the hard disk into memory, processed, and then written back to the hard disk.

CPU: The CPU is responsible for executing program code and manipulating memory. It's very hard to describe without getting too technical, but in general it's responsible for performing arbitrary tasks. I say arbitrary because specific tasks are often handled by other parts of the system in a more efficient manner. Some people like to compare the CPU to the human brain but I find that to be an inaccurate description. CPU's do not think, they do exactly what they're told to do and nothing more, they just do it extremely fast.

Chipset: The chipset is the set of hardware which allows the CPU to communicate with the outside world including peripherals, secondary memory (until recently it was also responsible for primary memory, but that has been moved onto the CPU by Intel and AMD), the system clock, and system management hardware. It's basically the CPU's secretary.

Graphics card: Graphics cards are very, very similar to CPUs and share a lot of the same architectural underpinnings. The biggest difference is that while CPUs are designed to perform one arbitrary task for a period of time and then switch to another arbitrary task, GPUs are designed to perform a number of very similar, simpler tasks at once in parallel (vector processing). Almost any task than can be performed by a GPU can be performed by the CPU, just slower; the same is true in reverse in that almost any task performed by a CPU can be performed by a GPU, just slower.

That's a very simple explanation of some of the core components. If you'd like a deeper one, feel free to reply or PM me.