With relay 2 activated, a press of button 1 activates the second relay. The second red light goes on, the shutter is fully pressed, and a picture is taken. If the camera is set in continuous mode, multiple images are recorded until button 1 is released.

Note that this works because I have set the jumber for relay 1 to "momentary".

If you press button 1 when button 2 is not activated nothing happens. It doesn't seem to hurt the camera, at least, but I avoid doing this.

PS if you set shutter lock, the first press of button 1 locks the shutter and the second takes the picture.