How do computers function?

Computers originated not so much with a technology but with an idea. That idea was that it is possible to break down complex activities, whether procedures or mathematical computations, into a series of extremely simple steps. Thus programmers develop "algorithms" that apply a series of simple steps to certain inputs to create outputs. 
The term "computer" originally referred not to machines but to people who did computations. Complex calculations, such as ballistics, were broken down into long series of simpler computations solved by large teams of "computers" (workers who performed computations). Gradually, machines were developed that could take the place of human computers, doing a series of very simple calculations very quickly.
Most modern computers input, store, and output binary information, i.e. strings of 0s and 1s represented internally as positive and negative electrical charges. Computers can perform a limited number of Boolean operations on either individual digits (the logical operator "not" which changes 0 to 1 or vice versa) or pairs of digits ("and" or "and not"). Computers are also capable of storing information in various forms of volatile or nonvolatile memory (RAM, disks), fetching information into processing units (CPUs), and processing information. Computers are also connected to input/output devices (screens, printers, keyboards, touchscreens) so that they can accept inputs and generate outputs.