After having explained this in an unrelated thread, I figured I might as well regurgitate it here, where it truly belongs.
Whether you choose "Insert Quote" (after highlighting text) or simply hit the quote button, in both cases the "Quotes" tab (red, bottom-right-of-page when you scroll to the bottom of it) appears and shows the bracketed number 1 (1). In the case of the "Insert Quote" option, the highlighted text is placed at the cursor position in the posting window. If you haven't started responding yet, it'll appear as the first-and-only entry in the bottom-of-page posting window.
Every time you do either of the above, the quote is added to the collection, which is thread-specific, and the aforementioned number increments by one.
To insert any or all of them, click the checkbox next to the ones you choose after hitting that red tab (it opens a pop-up window), and choose from the two options bottom-of-that-window - "Insert Marked Quotes" or "Remove marked Quotes". This way, you can pick and choose, and those you select for insertion will be placed wherever you've positioned the cursor in the posting window.
Even if you've submitted your post, you can still do a highlight-insert or conventional quote (with the button).
Make a highlight-insert quote, which of course will be added to a new posting window.
Hit the source-code button in said window (top-left of the function bar), copy the code for the quote, hit the "Edit" button for the post you want to add it to, engage the code display by clicking that code button again, place the cursor where you'd like to insert it and paste to that spot.
Then, when you hit the code button again to revert to the conventional-text display, viola! - the quote has been belatedly-inserted.
Same as option 1, but do a conventional quote. You can then use the quote-management tools to place it in a new window or at cursor position in the post you wish to edit.
If you place it in a new posting window, use the source-code trick to grab it and then place it where you wish in another post, as per option 1's instructions.
Why the source-code trick?
I've found that if you're wanting to add a quote from a previous page, for example, that things can get tricky. This is the easiest way I've found to get it done quickly.
Say you want to move a quote from the beginning of your post to the end. The quickest way, and you can select the response text as well if you've written any, is to hit that code button, locate the "offending" data, cut and paste it to a new position in the post. Hit the button again, and viola!
Using the source-code "trick" and the Quotes-tab functionality, all manner of quoting scenarios can be catered for.
Hope this helps someone!