If you hover over the ? it/the tooltip states 'Show help for selected item,' if you left click on the ? your mouse pointer changes to one with a ? next to it, click on a control part of the interface and you get a description of the control. I have to admit that I though that it should bring up the help file and according to the tooltip/s that is what it should do.
Left click on the ? and once the pointer changes, left click the ? again and the tooltip states, 'Displays avast! Program Help.' So I would say there is something wrong with the interface because that doesn't make sense as it is impossible to get what the tooltip states clicking on the ?.
However once the Simple User Interface is open the F1 key (default help key for many programs) brings up the help file.