Using a normal action on a button press lets you do a single thing, such as navigating to another slide, showing or hiding an image, or assigning a value to a variable. Advanced Actions let you combine a sequence of actions into one triggered event.
The Advanced Actions window opens up, with a blank advanced action started. Most of the window is taken up by the list of actions, with each row representing a possible action.
Above that you'll see some tabs, called Decision groups. If your advanced action has multiple conditions that it checks for, each decision group can contain a separate set of actions.