To toggle the display of non-printing characters (spaces, etc.), click the corresponding icon in the toolbar:
Special characters are a bit disjointed. The omega icon on the toolbar offers a few useful options:
However, if you need other characters, such as mathematical operators, copyright or registered trademark symbols, etc., you must go to Edit > Insert Symbol...
This opens the familiar Windows dialog:
Personally, I think this should be re-organized with that dialog also accessible under the toolbar's omega icon. I like the selection offered there, but adopting the "see more" approach of Microsoft Word would be helpful: