Referring to Users & Citing Parts of Comments

Today I successfully referred back to a user in a thread but had to painstakingly type out the /user name. Is there a quick way to copy someone's/username? Tap-hold doesn't work.

Also, what about text? People cite or refer back to previous comments someone made & pull the original text into their new comments to do it. How is that done?

Thank you for your help!

P. S. My account isn't brand new but I've only recently been active & am enjoying myself!