Folders always appear as a manila folder icon with a green folder name:
All of your folders (or lists) are always displayed on the left side in a list:
You can "drill down" by clicking on a folder name. The contents of just that folder are then displayed on the right side:
You can click on any one of the folders on the left side to quickly switch from folder to folder.
Lastly, by checking the "all folders" box in the show bar, you can cause all folders' contents to be displayed at once:
