it works in exactly the same way as an air filter on a car, exept your not using foam or paper to filter out dust, your using activated carbon to filter out smell.

the problem bein you have to somehow sandwich the carbon grauals between two porus barriers to make the filter work.

only one end is sealed, the other end is has a hole for an intake/exhaust, and then the air is forced to pass through the filter material, in this case carbon granuals, in the case of a car air filter, a foam or pourus paper structure.

picture shown is a performance car air filter, the same principals apply.