Arrange your carpet that you have measured to fit the room or area to be carpeted so that it can reach as close as possible to the perimeter on all sides, abutting the tackless strip.
Place the knee kicker with the prongs facing down into the carpet and toward the wall at a distance of a few inches.
Make sure that the prongs engage the carpet itself and hook securely. Otherwise you could end up smashing your knee kicker into the wall.
Use your knee to kick the rubber pad of the knee kicker, which will push the carpet out towards the wall. Hit the knee kicker hard enough to push the carpet over the tackless strip. The points on the tackless strip, which point toward the wall, will catch the carpet weave from beneath.
Move to a point in the room opposite your first attachment to make your second. Continue around the room in a balanced fashion, to avoid stretching the carpet too far in any one direction.