Cut the tackless strips to fit around the perimeter of the room. Lay the tackless stripes 2/3 the thickness of your carpet from the wall. Nail the tackless strips to the subflooring with carpentry nails.
Unroll your carpet padding. Cut the carpet padding to fit the width of the room. To create seams, overlap the padding and cut through both pieces so they are butting against each other. Tape 3-inch pieces of duct tape on the seams.
Staple the carpet padding down with a hammer stapler around the perimeter of the room. Unroll the carpet and allow the carpet fibers to expand for an hour. Push the carpet so the ends curl 6 inches up the walls. Press the carpet to the wall and flip over. Make a vertical line with a piece of chalk.
Cut the carpet with a utility knife. Overlap the carpet by 2 inches to create seams. Cut through both pieces so they butt up against each other. Apply seam adhesive to the edges of the carpets and press both edges together.
Place a knee kicker 3 inches from the wall. With your knee, press the knee kicker so it stretches the carpet to the tackless strips. Move over to the opposite sides of walls to stretch each side. Set up a carpet stretcher on opposites and press the lever. Tuck the ends of the carpet underneath the wall.