Here's an example of a simple LaTeX document:
The first line tells LaTeX what type of document; not surprisingly, the formatting of a document depends on the what type of document you are creating.
You should use "article" for most documents. Some other choices are book, report, letter, exam, and minimal.
The second line tell tells us where the document begins and the fourth line where it ends. In between the beginning and end (the 3rd line) is the document. You can change it to whatever you want to create your own simple document. Here's the Gummi output from the code above. Notice the IDE shows the line numbers and in the pane on the right shows the output as well.
It's worth mentioning that LaTeX has made a lot of decisions for you: the margins, the font, the color of the font, the fontsize, the space between lines, the space between paragraphs, and more.