For an automatic the slap stick is pretty simple. (I once had a Camero with one)
With an automatic you usually need to press something on the shifter in order to get it to shift from one gear to another.
Basically there is a piece of metal with a series of notches in it. There is a flange attached to the shift that rests in any of the notches. each notch is at a gear position like thus:
Now you still have to push the shifter to leave park, but from reverse or neutral all you have to do is "slap" the stick back until it drops into drive. (but notice that if you slap the stick forward from drive you only can get as far as neutral; which prevents you from accidentally knocking the car into reverse while driving down the freeway.)