That's used for smoking, where you would have the fire and coals in the side box only. The heat and smoke cook indirectly. It's also useful for long-term grilling if you need to have hot coals for a long time. You can keep putting fresh materials in the box to make more coals to move into the grill. The owners' manual should give you some ideas to get you started.

So I could smoke a turkey using only the firebox? Thanks for your reply "purpleinopp".

Since my grill doesn't have the firebox, I couldn't confirm this or give you instructions, but in theory, yes you can.

Try some of the links:

Here is a link that might be useful: google

I always wonder why people like you post replies that say absolutely nothing- you don't think I know how to google? I wanted the experience of GardenWeb members to answer my questions- but none like you. Here's a link for you-
http://www.fanpop.com/spots/sarcasm/links/1592359/title/75-sarcastic-remarks

purpleinopp, you have my sincerest apology- I have since learned that your link was more than just google- sorry, I was to quick to jump to conclusions but now realize you were trying to be helpful!!
Regards
Paul