A digital computer, such as a PC or NES, is filled with millions of tiny switches that can be turned on or off. Some switches store information for short time; these are called memory. Other switches calculate things based on the output of other switches; these are called logic. Each switch can be on or off, representing true or false, or the numbers 1 or 0. Multiple switches grouped together can represent larger values. A CPU reads machine code from a memory and treats it as instructions to perform arithmetic and logic operations on other values in memory or to perform input and output. Some of the input and output involve user interaction: the user gives commands to the computer, and the computer displays the result.
If you're confused, now is the opportunity to become familiar with the following basic concepts from computer engineering and computer science. These articles from Wikipedia are in English, and many have been translated into other languages.
The Nintendo Entertainment System has the following components:
Cartridges have the following components: