You met these in the introductory tutorial and there is not much more to learn.  A div element is like a container, a box.  It is used to hold other things.

Open media.html in your editor.  Also view it in a browser.  Fairly close to the top of the code you should have two images (img elements).  Before the second one add <div> and after it add </div>.  You now have two images:

image 1

start div

    image 2

end div

Save and view the page and the images should now be on different lines.

In-line and block

Images are known as in-line elements.  They will be displayed one after another in a line.  Paragraphs and divs are block elements.  They get a new line.  Paragraphs and headings are also block elements so they get their own line as well.

A block is an area of the page which by default takes the full width of the page.  An in-line element uses only as much space as it needs.

For now just remember this as it will come back later.