Text that is copy and pasted into the TinyMCE editor can contain some extra HTML formatting code that can affect how your text will appear in Moodle. Here are some tips to prevent and to fix formatting within Moodle.
Highlight the text that has formatting you wish to remove with your mouse
OR
Highlight all text (Same as Ctrl + a on your keyboard)
Click the 
Clear Formatting button
Repeat as desired for any chunks of text
Save your changes
This can be used to copy just the text from another location into your text editor. It will strip all the formatting so you will have to reformat your text editor tools.
This issue rarely occurs in Firefox. Consider using the Firefox web browser if you’re developing a lot of content in Moodle.
If you want to use Chrome you can either enter text directly into the editor (not recommended for lots of content) or you can paste content into the editor WITHOUT it’s formatting though use of the Special paste button (or Ctrl + Shift + v on your keyboard).
If your content did NOT come from MS Word, gDocs, or LibreWriter you can preview effectiveness by opting to Paste from Other (when possible) or Paste as unformatted text to get a fresh start on formatting that’ll remove even headings and links.
If you’re rearranging content in your course consider
You can also strip formatting from text but there are some things to keep in mind before you do so:
Built-in tools can be limited and will only know how to fix certain issues.
If Paste text and Clear formatting aren’t enough to fix the formatting of your content please submit a ticket to OLET via Online Learning/Moodle Support. Make sure to include a link to the content and a description of what the issue is so we can manually clean up the HTML code for you.