Virtually everyone these days uses a graphical window editor with menus, running in a modern operating system that uses windows, icons, and a mouse which moves a pointer. This probably works fine 95% of the time, when you're dealing with one document at a time, and everything you want to do is accessible through the menus, and you explicitly don’t want to see LATEX spilling its guts all over the place every time it reformats the document. Click here, move to there, cut, move somewhere else, paste, edit the text, write some more, click and you're done.
This wasn’t always the way of working, though, and for a small but significant number of people, running LATEX manually is still the order of the day. Maybe they’re working on a giant mainframe or supercomputer with no graphics, just a 3270 terminal. Maybe they're using a tiny smartphone where the editing facilities are poor and the scope for full menus entirely absent. Or perhaps they are simply uninterested in all the bells and whistles of the modern interface, with too many menus doing things they can type faster by hand.
Before I go any further I’m going to assume at this stage that you have typed some sample text in the format specified (for example Figure 1.2), and you’ve saved it in a plaintext file with a filetype of .tex and a name of your own choosing.