The practical answer is: you drive as far as you legally can.

As a disclaimer, pictured here are the Himalayas, which are at a completely different scale to where I've been, but in my experience there are typically parking spaces/bus stops at the end of public roads. At this point you leave the built up infrastructure and enter nature, and these are often located in a place where the flatter valley ends and a steeper ascent begins. In many cases there are smaller private roads further up to service more remote cabins or farmsteads. Sometimes there are even taxi services that drive you further along using private roads, which can be seen as not fully scaling the mountain yourself. Generally, the closest public parking is considered the starting point and most people will therefore start at the same spot.