Measure the doorway. Cut the carpet tack strip to the length of the doorway using a saw.
Place the tack strip under the carpet 1/2 inch from the line where you will place the transition strip. Use a hammer and one nail every 4 inches to secure the tack strip to the subfloor.
Use an old board to stretch and pull the carpet over the tack strip. Press the carpet into the strip to hold it securely in place. Use a utility knife to trim the edge of the carpet.
Use a jigsaw to cut the carpet transition strip to the length of the doorway. Place the strip on the edge of the carpet.
Hammer the transition strip to the subfloor using the nails that come with it.