The WYSIWYG ("what you see is what you get") editor is the interface we use to edit our pages in Drupal. It allows us to see, more or less, how parts of our pages will look as we are working on them, and gives us a few options to modify our content. We can add some text formatting, bulleted or numbered lists, links to other pages or sites, indents, headers, etc.
Plain text
You’ll see many icons as you work your way through Drupal screens, but a good one to know right off the bat is the little yellow clipboard with the blue dot towards the right-hand side of a WYSIWYG text box’s menubar. That’s the Paste as Plain Text button. You’ll want to use that whenever you aren’t creating content right there in the editor, like if you’re pasting text from somewhere else. The reason is that other applications (especially Microsoft Word) are notorious for bringing in their own formatting that wreaks havoc when translated to the web. Start clean and strip out all that stuff, and your content will be pretty no matter what device or browser your users have.