Keyboard -these are pretty well standardized and have been for years
Mouse - unless you want a trackball
Printer - most use inkjet because of cost, but if you have to have the highest quality output, look at a laser printer
Computer - usually called the CPU box, system box or tower
Cables to connect anything that isn't wireless. Keyboard and mouse will have the cable built in, unless they are wireless.
Inside the computer case will be a power supply, a motherboard, at least one hard drive, and either a CD or DVD drive. Extras include a graphics/video card for the monitor, ethernet or wireless LAN card, sound card, and cards that add memory, processing power, or extra ports.
On the motherboard, the options are in the size and speed of the CPU, and the amount of RAM.
The first thing to do is to determine what you are going to use the computer for, and which software packages you will use to do it. Then, get the hardware to match the software manufacturers' recommendations, and actually exceed those recommendations, or make sure the hardaware can be expanded or upgraded to meet unexpected needs - and WANTS!
Always remember, that to err is human, and you can really screw things up with a computer!
__________________
I wonder..... Would Schrödinger's cat play with a ball of string theory?