Oh I see. Just me and my English again, I just don't pick up some words...
If you put your lips forward, but not so much that it's uncomfortable, so that you'll look like a stupid duck, and then whistling inwards, you'll get a loud and clear sound.
My mom whistles with the hole a little to the left.
I can whistle very loud with a little help from my index finger and thumb on both hands. I put the four fingers together forming a small square about 6 mm big, and blow through that.
Gard