pic: Planetary Gearset

[KenWittlief]

in an automatic transmission like this in a car, there are clutch mechanisms, called bands, that hold one set of gears still, to get the ratio you want to the output

and dont forget, the torque converter in a car is not only a slipping clutch, it is also a form of hydralic CVT itself (its like a backwards CVT - the motor can vary over a range of rpms while the drive wheels are at a constant speed)

You can get more HP out of an automatic transmission off the line, than you can from a standard one (with a clutch) because the auto can rev up to its optimum RPM

very similar to the problem we face with electic motors - to get the most HP they have to be spinning at the midpoint of their RPM range