To put a folder of bookmarks in the bar or menu:
Click the open-book icon to show all your bookmarks.
In the left column, click either Bookmarks Bar or Bookmarks Menu.
In the left column, find the folder you want to add to the bar or menu, and drag it to the column on the right.
If you put the folder in the bookmarks bar, you can have all the bookmarks in the folder open as a set of tabs whenever you click the folder in the bookmarks bar. To do so, select the Auto-Click checkbox next to the folder’s name.