CKEditor allows viewing the written text in the editing area in the HTML code.To see the HTML code user should press button on the toolbar.
Example:
File:CKEditor example source.png
After pressing button HTML code is shown:
Image:CKEditor_example_source2.png
To go back to the normal text press again.
Editing the code in the HTML language is a very difficult feature and it should only be done by advanced users. If you do not have experience in HTML type the text normally.