The Rich Text Editor item in Application Express allows to edit formatted text - unlike the simple textarea item which just allows to work with plain ASCII text. The rich text editor generates the formatted text as HTML code and sends that to Application Express on page submit. Most applications then simply store that HTML text into a database table.
CKEditor offers many tweaks to control, how the actual HTML code will be generated from user inputs. For instance, hitting the Return key by default produces a new paragraph with the <p> HTML Tag.
We can change that - now we want to have the editor produce simple line feeds using the <br> HTML Tag.
If you don't like the toolbar options which are provided by Application Express, simply configure your own set of options.
In CKEditor's API documentation you'll find much more attributes and explanations how these work. It's advisable to invest some time into this - at the end of the day you'll be able to get a Rich Text editor as your application requires it. All functionality can be leveraged. But there is much more than this: when combining this elegantly with other APEX pages, dynamic actions or REST services, we can extend the editor with things like an image upload capability, we can make is responsive and much more. To learn about this, read the full community article here.