Ginsue, it goes inside the smoker, and rests on the rails coming off the side of the built in smoke box.
It is really not very big, but puts out a great amount of smoke inside the MES. It will run for as long as I want it to overnight, putting out a nice thin blue smoke.
With the built in chip loader, I had to add more chips or pellets every hour and a half, and sometimes it didn't want to make smoke for me. It worked better if you preheated the whole unit to 275 degrees at the beginning, but it really was pretty lame overall.
The AMNPS turns a stupidly easy to use smoker that makes "meh" BBQ into a very good smoker. It's really set it and forget it until it's time to eat.
When you use the AMNPS, halfway open the inside chip tray, and the outside chip loader for increased airflow, and leave the top vent fully open. Works for me all 4 seasons here in Lakewood, you just need to know a simple trick to get the MES to kick on when the outside temps are below 32F.