How to rotate the 3D view

Super-simple question… In the 3D view, I see the board lying flat and can pan around and zoom in/out. Your screenshots suggest it’s possible to rotate it to view in 3D rather than just looking straight down. But what’s the control/key/gesture I’m missing to be able to do that? I spent some time experimenting, and it’s definitely not obviously discoverable!

Try to drag mouse with right button pressed down.

Is that possible with a trackpad on OS X? I can get a right click event with a two finger tap, but dragging with two fingers just sends horizontal and vertical scroll events.