Instead of explaining what the LaTeX software itself is, it shoud be mentioned that without third party programs, the user can't create anything. Before the latex command line tool can be started, the text has to be created in a text editor. There are not a single but a lot of external text editors available:
- emacs with latex plugin, vim with latex plugin, texnic center, overleaf, Lyx, texmaker and many more
It is interesting to know, that latex users are not starting latex itself, but they are using both. The text editor and the latex backend. It is possible to find similarities between the mentioned editors. What they have in common is, that they can be classified as advanced outline editors. The reason is, that all of them are providing on the left pane a hierarchy tree with the document structure. In the right window the sections are shown and sometimes the latex preview is shown in a third pane.
So what is the idea? The idea is, that the user creates notes in a plain text format. Then the notes are structured into chapters, and then the text is rendered into a scholarly paper.
From an abstract point of view the idea behind texnic center, lyx and overleaf is, that the user types in structured plain text and doesn't care about the formatting. If the text file has reached a certain size for example 200 kb, the user can render the file into a pdf file.
The latex community describes this workflow as seperation between content and layout. Before they are formatting the document into a pdf file, they are taking care of the content. LaTeX allows much better than other typesetting systems to divide the article creation process into these two sub tasks.