If you’re referring to the top set of buttons, these are iOS-only, and would just copy the raw text to your clipboard. The Copy button next to Quote and Edit in this case copies the Discourse markdown of that quote, which looks like this:
[quote="JammyDodger, post:7, topic:285376"]
Possibly a silly question, but what’s the difference between this button and the one I get normally?
[/quote]
If you press Quote, then the composer opens with this prefilled, but a lot of the time you don’t want to quote the selected text in the current topic as a reply – you may want to quote it in another topic draft that you already have, or in chat.