It might look something like this:
This is usually the result of cut and pasting from Microsoft Word or another external application. When cut and pasting from Word, make sure to use the “Paste from Word” button in the rich text editor. This will strip any formatting and leave you with nice, clean text.
If you are cut and pasting from another application (such as an email), the “Paste as Plain Text” button (located to the left of the “Paste from Word” button will also come in handy.