Make sure your listing shows all the items you can view. The page navigation control is at the bottom of the screen, and there may be more than one page of items.
Make sure your list displays all the files and folders you can access. Click the menu next to the heading and select All Files. To change your viewing list, click Shared with You or Owned by You.
If you're looking for a shared folder, it should appear in your folder list with a shared icon. Contact the person who shared the folder to make sure the invitation to share was sent and that the folder is still being shared.
If a folder was shared with a public link, it won't show in your listing as a shared folder. You can only access that folder via the public link.