Here are a few items you're sure to see if you watch the installation process!
Tack strips are slats of wood nailed to the floor around the outside edge of the area where the carpet will be installed. Each strip has angled pins sticking off the top designed to catch hold of the carpet and keep it in place, allowing it to be stretched tightly into position.
The knee kicker is about a foot and a half long and has teeth at one end that grip the carpet. The installer sets the kicker onto the carpet and strikes the pad at the other end with one knee. This pushes the carpet forward, stretching it into place.
The installer uses the seam roller to press down on the seam between two pieces of carpet, attaching them to the adhesive strip underneath. This creates a tight seam that is essential to the life of the carpet, especially in high-traffic areas like doorways or stairs.