From FCKeditor Docs

This function determines what functions will be available to access from the toolbar. It also points out their arrangement on the toolbar. The syntax of the function

• Functions are divided into sections by placing them inside square brackets " [ ] ".
  

  ['Source']

• You may separate functions inside the section by putting a " '-' " sign beside them. It will appear as an pipe (|) in the toolbar.
  

  ['Source','-','DocProps']

• If you want to start a new line with functions put " ,'/', " between the section.
  

  ['Source','-','DocProps'], '/', ['Bold','Italic']

• Remember there is no comma after the last row.

Full Code:

FCKConfig.ToolbarSets["Default"] = [
['Source','DocProps','-','Save','NewPage','Preview','-','Templates'],
['Cut','Copy','Paste','PasteText','PasteWord','-','Print','SpellCheck'],
['Undo','Redo','-','Find','Replace','-','SelectAll','RemoveFormat'],
['Form','Checkbox','Radio','TextField','Textarea','Select','Button','ImageButton','HiddenField'],
'/',
['Bold','Italic','Underline','StrikeThrough','-','Subscript','Superscript'],
['OrderedList','UnorderedList','-','Outdent','Indent','Blockquote'],
['JustifyLeft','JustifyCenter','JustifyRight','JustifyFull'],
['Link','Unlink','Anchor'],
['Image','Flash','Table','Rule','Smiley','SpecialChar','PageBreak'],
'/',
['Style','FontFormat','FontName','FontSize'],
['TextColor','BGColor'],
['FitWindow','ShowBlocks','-','About'] // No comma for the last row.
] ;