Cut the edge of the carpet if it is has not already been cut. Use a utility knife to cut off any fraying or uneven parts. Ensure that you do not cut too much off, leaving too little to fit under the strip.
Fit the threshold strip in the doorway so that the edge of the carpet is securely underneath it. Place the angled part of the strip on the side where the door closes. Hold the strip secure and close the door to ensure a proper fit. Adjust the strip as needed to make it fit.
Insert a finish nail into each hole in the strip and pound them in at a 90-degree angle using a hammer. Be careful not to hit the strip with the hammer as the nail is driven closer to it.