It sounds like you have an "offset smoker". The fire goes in in the firebox (the small offset box). If you have a rack that fits in the firebox, you can put that in there too and use it to grill.
Go to
www.charbroil.com and click on "instruction manuals" and find the manual for the one that looks the most like yours. Char-Broil took over New Braunfels a few years ago.
Once you have it assembled, there are huge resources on the web on how to use it.
Personally I rarely use charcoal, I prefer the taste of cooking with Pecan wood - if you live in Texas you can buy a 50lb bag at Academy for about 10 bucks.
I grill over the firebox part directly (although I often close all the dampers and let the meat smoke a little while cooking). A few times a year I'll smoke a turkey or other meat in the main chamber, keeping the fire in teh firebox.