Just navigate to the page and click on "Edit Page". The WYSIWYG editor will open. You can toggle between WYSIWYG/HTML view.
LightNEasy uses an embebed TinyMCE editor. For more informations on how to use TinyMCE editor, please go to the TinyMCE webpage and read the documentation.
After you edited your content, press 
to save and exit, or 
to exit without saving. 
will toggle between WYSIWYG or code view.
Note: while on WYSIWYG mode, TinyMCE will filter out any HTML code you enter. If you want to include a special HTML code in your plage (like an embeb code for a remote applet), toggle WYSIWYG mode to code view, enter your HTML code and save the page without toggling to WYSIWYG mode again.
Note: in the settings menu, "Gzip" is 0 by default. If your webserver supports GZip compression, the load time for the WYSIWYG editor will be significantly shorter if you set it to 1. Or it doen't work, in which case you just set it to 0 again.