Here are the steps on how to fill the gearbox fluid in a VW Golf Mk4:
1. Park the car on a level surface.
2. Turn off the engine and allow it to cool down.
3. Locate the filler plug on the side of the gearbox.
4. Remove the filler plug.
5. Insert the funnel into the filler hole.
6. Pour the gearbox fluid into the funnel until it starts to overflow.
7. Replace the filler plug.
8. Start the engine and let it run for a few minutes.
9. Check the gearbox fluid level again and add more fluid if necessary.