I just found the solution in another thread. You need to hit Menu -> Folders which lists the top-level folders, in particular "Inbox". Then in order to see the subfolders on Inbox, you need to click on the folder ICON to the left of the work Inbox. Do not click on the word Inbox, since that will just cause Galaxy to display the email in your Inbox folder. However, clicking on the folder icons allows you to navigate through the email subfolders.