A typewriter is a mechanical or electromechanical device with keys that, when pressed, cause characters to be printed on a medium, usually paper. 
(Typewritter existed before the computer was invented).

Typically one character is printed for keypress, and the machine prints the characters by making ink impressions of type elements similar to the sorts used in movable type letterpress printing.

After their invention in the 1860s, typewriters quickly became indispensable tools for practically all writing other than personal correspondence. They were widely used by professional writers, in offices, and for business correspondence in private homes. 

By the end of the 1980s, a psychological change and revolution began to take form, word processors and personal computers began to replace typewriters in most of these uses.

End of an era:

The 1970s and early 1980s were a time of transition for typewriters and word processors. In a given year, most small-business offices would be completely old-style, while large corporations and government departments would already be all new-style; other offices would have a mixture. 

The pace of change was so rapid that it was common for clerical staff to have to learn several new systems, one after the other, in just a few years.