I believe you are talking about the baskets used in a side firebox or WSM.
These are to hold charcoal in a neat pile. You fill the basket or ring with unlit charcoal that has smoke wood mixed in. Make sure that there is as little air space between briquettes as possible. Put about a half chimney or less of lit fuel on top and close the vents down to control the temperature as it reaches your target temperature. Be careful to not let the temperature climb too high because once the fuel gets burning it's difficult to bring it back down. This is referred to as the "Minion Method" and can be found in more detail at: