Processor – This is the brain of the computer. It is a large chip that sits on the motherboard that controls all the different parts of your computer. The 2 companies that make processors are Intel & AMD. I would use either brand in my computer but not any model. Both brands make different models and they are priced so that the cheap processor is also the slowest.
Memory – aka RAM – This is the “workspace” of your open programs while the computer is on. The more programs you have open at once the more memory you will use up.
Hard Drive – aka disk space – This is the storage space on your computer. All files & programs are stored on your hard drive. If you turn off your computer and move your hard drive to another computer your files will still be there. You cannot run most programs on a different computer after moving a hard drive, but all your photos, music, Word, Excel…etc files will be accessible on the new computer. These files are important to backup to an online service (on the web), a thumb drive or external hard drive because if your hard drive stops working then your files are usually gone forever. Hard drives are usually the first part of a computer to quit working due to the constant movement of their internal parts while the computer is on. A new type of hard drive that is starting to be available is a Solid State Drive (SSD). It does the same thing but has no moving parts which makes the them react faster, work more efficiently, using less power & giving off less heat…all great things but they come with a much larger price tag.
Motherboard – This piece holds and connects all the other pieces. The processor and memory plug directly into the motherboard. The hard drive is connected to it via a cable.
There are several other parts to a computer but the first 3 above are the ones you will need to know a little about when shopping for a computer. Hopefully these short explanations will help you understand them a little better.