You can quote from previous posts or other sources by simply selecting original text in your browser and either using ‘Copy’ from the ‘Edit menu or by using "Ctrl" + ‘c’ then by choosing ‘Reply’ and positioning your cursor in the window then pressing ‘Ctrl’ + ‘v’ or choosing ‘Paste’ under the ‘edit’ menu.

To distinguish your quotes from your own text, simply preceed them by <<< and follow with >>> Like this:

<<<This is a quote >>>