It's actually quite simple. Place your filler tube on top of the punt or bottom if there isn't one and fill to top of bottle. Close off via the plastic clamp and remove from bottle. The displacement from the tube will equal the space recommended for wine.
When you get good you won't have to clamp off just have good aim from one bottle to next.
Not wanting to start another thread but what is the air space needed for beer? I'm going to bottle my skeeter pee in some Samual Adams beer bottles with a crown cap and wondered how much space is needed. 1/2 inch, 1 inch. Does it really matter with s.p.?