The forward clutch is applied, locking the input shaft to the ring gear. All planetary gear members are locked to each other and to the output shaft. In reverse mode, the reverse and high clutch is applied. The input shaft is locked to the reverse and high clutch drum, the input shell, and the sun gear. These are the basic workings or a Simpson transmission.
Some cars use a multiple-disc clutch operation.
In this setup, a series of friction discs are placed between steel plates. The clutch also has a piston and return springs. This whole assembly is known as a clutch pack. When fluid pressure is applied to the clutch pack, the piston engages, locking the assembly together and driving the wheels. Other cars use transmission bands.