A robot is a machine capable of carrying out complex orders.
A barcode reader is a device that reads barcodes, which can be found on most brick-and-mortar store products.
I don't know what you mean by expansion slots.
A motherboard is a device that houses your RAM, your CPU, and your GPU. It also does other things as well, but those are the most important.
For the system unit, I'm going to assume you mean the case. The case is what holds the motherboard and the power supply. It also stores slots for additions, such as CD readers and thermometers (the thermometers are used to make sure that the computer doesn't overheat)
RAM, or random access memory, is temporary storage that gets dumped. It's used for programs that are currently running.
ROM is read-only memory, used mostly in video game cartridges. It can only be modified slowly, or sometimes not at all.
A processor is what processes information. They have cores, and the cores have threads, but explaining that would take a while.
I don't know the others, though.
