The standard WYSIWYG WordPress post/page editor is mediocre at best.
While it gives you the basics to add and edit content in your posts and pages, it is really can be a pain to work with overall. TinyMCE Advanced plugin is the solution to that. Beef up your editor, and get some really cool functionality, that gives you more control over editing and formating your website content.
Get the TinyMCE Advanced plugin here: TinyMCE Advanced.