Huge blocks of featureless text can be not only dull, but also very difficult to read.  Reading from a computer screen is a very different experience from a printed page, after all, and visual landmarks can help the eye track down the virtual page.

First and foremost amongst the ways one may break up the flow is to use paragraphs.  In CKEditor this is as simple as pressing Enter.  The editor will automagically close the current paragraph and open a new one.  As browsers render HTML, this puts a one-line break between blocks of text.

This is a very short paragraph.

This is a shorter one.

Simple enough, yes?  Making use of paragraphs is a good start, but we can do so much better...

Let's talk about headings

The preceding line is a heading.  Specifically, it is a level 2 heading encapsulated by <h2> and </h2> tags.  Headings get their own line and are (generally) displayed in a manner distinct from the normal body content that surrounds them.  Not only do headings help break up the monotony, they also help some of the more advanced web indexing engines understand the page content.

Headings come in six sizes:

Heading 1

Heading 2

Heading 3

Heading 4

Heading 5

Heading 6

As you might be able to tell, level 6 headings are almost identical in size to normal body content (like that found in a paragraph).  Browsers differ, however, so one can never tell.

To turn a bit of text into a heading, simply place the cursor on the appropriate line (highlighting isn't necessary), select the appropriate heading from the drop down, and everything in that block of text becomes a heading.  Simplicity!

On that note, HTML is really considered a series of suggestions about how to display a site's content.  Most types of styling can be overridden by local settings and images can be excluded, for instance.  Always remember that what it looks like on your screen is not necessarily what the end user is going to see.  So much for "What You See Is What You Get," eh?

Moving on...

Using only paragraphs and headings, a content creator should be capable of producing material that is easy on the eyes.  However, some authors may like to emphasize certain points or otherwise make some things stand out.

Bold, italics, underlines, and strike through's (or a combination, thereof) may help with that.

Adding such font effects is as simple as highlighting the text you want to style and clicking the appropriate button on the toolbar.