One instructor's explanation was this, kind of a toe the line and slide all in one:
Stand behind the shot and lay your cue on the table with the tip right behind the CB and the cue pointing right down the shot line while still holding the butt in your grip hand.. Turn your body about 45 degrees and place your back toe or heel(preference) on the shot line indicated by the cue. Now, keeping the stick pointed down the shot line slide your front foot forward while sliding your bridge hand under the stick to the appropriate distance from the CB. Not saying I like this, but it's what he taught