Copy a highlighted content, paste it into the comment field with a button...?

I'm asking for a coder who doesn't know much English.

We're designing a kinda blog website. It should have a feature like this: when a viewer is reading an article, there is a toolbar on the side, which has some hotkey buttons - for example, 'Q'. If the viewer encounter something interesting and want to quote it in their comment, they just need to highlight the thing using the mouse and then press Q. That will copy the thing and paste it in quoted form into the comment field at the bottom of the page. Also, the pointer-cursor will be placed right at the end of that quote, ready for the viewer to type the comment. Which means it has 'disconnected' all the possible conflict inputs with the toolbar.

How do we do that? Thanks!