This editing toolbar is also commonly known as the WYSIWYG ("What You See Is What You Get") toolbar.
The first line includes various editing options that you can use to format your content: bold, italic, bullets, links, media, etc. If you click the button on the far right side ("show/hide toolbars"):
This will expand the toolbar and show many additional editing options, such as headings, copy/paste options, table options, etc.:
The additional pages in this section (see menu on the left) will provide additional information on specific options available in the WYSIWYG.