Your moon dial pipe will fit over the hour pipe and is regulated by another wheel that runs off the hour pipe. It has a spring resistance lever that engages that new wheel and applies pressure so it can't change until forced by the hour pipe. It activates the moon dial every 24 hours. After you get the gears in place, run the minute hand around until the moon dial is activated. At that point, set the hour hand at 12, and the minute hand at 12 (as close as possible - on the hour). Manually lift the count hook and repeat until it strikes 12 times. This is "midnight" setting. Now move the hands until the current time is set, adjusting from the "midnight" setting (in other words, it may be more than 12 hours off). Now you're set, and the "moon" should change at about midnight every night. Follow Mikes post on where to set the moon dial (just manually pust it until it's right. If it resists, it's because it's near the "midnight" setting and meeting wheel resistance). There you go
Another method, and one I tell my customers, is to advance the moon dial one click for each day past the new or full moon. For example, if the full moon was on Nov. 5th and it is now Nov. 18th, rotate the moon dial until the whole moon can be seen in the window and then advance the wheel 13 clicks.
These moon dials aren't extremely accurate and will need to be reset periodically.