I Require Help With Carbon Filters

Ok so here is what I DO know.
-The carbon "scrubbers" absorb the smell!
- The filter is a part of the exhaust and filters the air so that the final exhaust stage (the release of the air) releases regular/clean smelling air
- Ability of filtration is based on surface area
- Eventually, the carbon is "used up" (stops filtering as well or at all) and you must replace the carbon inside with fresh carbon.
- Oh and the carbon is, "activated carbon". I dont know exactly what that means.
What i dont know, and need to know
- Where does the filter go?? Is it on the inside or outside of the grow room?
- On titles of the carbon filters (i.e. an amazon listing), it has a CFM rating. Does this mean the filter itself has a fan in it? If not, why the CFM?
- If no fan built in (im pretty sure there isnt one built in), does the fan go on the entering or exiting end of the filter?
( Exhaust Air Exit <-- Ducting <-- Filter <-- Outake/Exhaust Fan <-- Contained Grow Area )
^ annnnnnnd this ^ (which order) make sense?
- anything else i dont know about it, feel free to add whatever.


Thanks.