Hold button
 

I got a 1.5DOHC auto protege..
and it has a hold button on the gear knob
how does it really work?

Its OVERDRIVE/OFF button. Its a feature designed for automatic trannies, where if you are hauling something, and want the gear changes to be just a bit longer, and loose the 4th gear, you would turn OVERDRIVE OFF. I never found use for it, well, maybe when braking, if you go about 40-50, and begin to slow down, by turning OVERDRIVE OFF it automatically shifts one gear down, thus engine braking. I think this is the only way you can imitate engine braking with an automatic tranny.

oh....sweet as....
it is useful when i go round a curve at high speed?

shifting to 2 is also a good alternative for braking and manuvers where you need engine response. just dont shift while accelerating, coast into a shift.