On admin panel, click on your name on the top-right menu and choose "Saved Responses"
Then click on "Add"
Fill up the form , choose an icon for the shortcut if you wish to have.
Once filled, you can choose if this shortcut is visible while replying to the customer on a ticket or on live chat , or both.
The shortcut will be visible on the top of the reply textbox in Ticket area, and on the bottom of the text box in live chat