The charcoal basket is for inside the firebox. Basically it lets you load a larger amount of charcoal while keeping it from plugging up the air vents. Most people use the minion method with the baskets: fill the basket 2/3 to 3/4 full of lump charcoal or briquets, then light a full chimney of more lump/briquets and dump it into the basket once it is going.
If you have a charcoal pan in the main chamber that hangs below the cooking grates you can flip it upside down and use it as a tuning plate. Basically you are wanting to force the heat to travel the length of you cooking chamber below grate level as much as possible before it heads out the stack. Other wise the firebox end gets real hot, and the heat (and smoke) go straight up out of the firebox to the roof of your cooking chamber and out the stack... missing the meat.
Also extending the chimney inside the smoker down to the cooking grate level also helps to make sure that the heat and smoke travel across the meat before leaving the smoker.
If your tuning plates are slightly lower than the opening to the firebox, a baffle is used to deflect the heat down under the tuning plates. Basically it is a piece of sheet metal attached just above the firebox opening that angles down and drops the heat under the tuning plates. Use cardboard to create a pattern and then get some sheet metal, tin snips, and rivets to cut out the baffle and rivet it to the smoker.
If you poke around the charcoal smokers forum there are pictures and examples off all of this that will help give you a better visual.