I'm far from an expert so far but autos get a lot easier once you've been inside of one and rebuilt it.
Drums are just housings for hydraulic pistons and clutches.
Pistons are just hydraulic rams that apply pressure to clutches.
Bands are just clutches that wrap around a drum that get squeezed together to stop the drum from spinning.
Servos are just hydraulic rams to squeeze the bands.
Accumulators are just reservoirs to store fluid in that eventually is used to hasten the time it takes to fill the space behind a piston. If there wasn't an accumulator it would take too long to actuate a piston all the way.
Once you get in there and realize what is happening its all just basic hydraulics.
The real magic is in the valve bodies. The people and companies that know enough to modify those are the true geniuses.
