A: You can...
...open boxes with a shadow. Try it out on this box! Currently, box 'A: You can...' is selected. Open it by double-clicking. You can also make a tap-and-hold gesture (long press) on the box or press the 'Open' button.
Opening a box will take you down one level (deeper into the details). This will reveal another map with boxes. Such a sub-map explains the current topic in more depth.
By the way, you can recognize if a box can be opened by the shadow around it. It looks a bit like two cards stacked on top of each other