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1, Open Nautilus and select bookmars -> edit bookmarks, or simply press Ctrl+B to edit bookmarks.
2, Open Nautilus and drag and drop folders you would like to have in Places menu to the left panel.
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3, For the console ninjas there is another way of doing this in command line. Configuration file for Nautilus bookmarks and places menu is .gtk-bookmarks in your home directory. Just edit the file and you're good to go. My fave editor is vi - so I will use that as an example, but you can use whichever you like.
$ vi ~/.gtk-bookmarks
One more tip - to alphabetize your bookmarks
$ sort ~/.gtk-bookmarks -o ~/.gtk-bookmarks