Copy and paste on Facebook

Hello SarahElfeky, 

Thanks for reaching out to the Apple Support Communities.We understand that you'd like to know how to use the Copy feature in the Facebook app. 

Copy and Paste works the same across applications, as shown in this article: Select and edit text on iPhone. 

There are some apps and websites where you may have to select text in its entirety, and not just a single word.  If you're having issues with not being able to copy anything in the one specific application try these steps: If an app unexpectedly quits, stops responding, or won’t open. 

All the best.