what is a computer? (wikipedia)

A computer is a machine that changes information according to well defined rules. Computers have existed for much of human history. Examples of early computers are the astrolabe and the abacus. Modern computers have changed very much. They are able to control traffic lights, cars or locks. Most modern computers can be used to play music or video. The basic principle is still the same though: the computer has a set of rules, usually called an algorithm. The computer changes information based on these rules.
A person uses a computer by telling it to do things, like playing movies or going to Wikipedia. Computers do not know English, so people must tell their computers to do things by speaking the computer's language. The computer's language is called a programming language. Programmers know this computer's language, and use it to write programs that tell the computer what to do. Normal people use the programs that a programmer wrote to tell the computer what to do.
Computers can do anything that someone can tell them to do. Computers are able to solve mathematical problems because a programmer has told them how to solve math problems. Because computers are very fast, modern computers can solve billions of math problems per second. Computers are used to control factories, which in the past were controlled by humans. They are also in homes, where they are used for things such as listening to music, reading the news, and writing.