The first step is to decide what program is best suited to the task in hand and use it to create the document. The result of this process is a file containing a complete description of the document. This description is, in general, a form of GRAPHICS LANGUAGE. The most popular one in the subdepartment is Postscript. The document software sometimes offers support for more than one language.
Some documentation software provides a What You See Is What You Get (WYSIWYG) interface. Such programs run in full screen mode and allows you to see immediately what the final document will look like. An example of such a program is Microsoft's WORD. Other software does not work like that. You create a file (with any word processing editor) which contains all the document material together with commands to the software instructing it how to lay out the document. An example of such a program is TEX. Not being able to see the final result at once is a drawback but there are advantages; making changes that have a major effect on the layout may be quicker and, as the files are plain text, they are easy to move from machine to machine.