In the video, a person is seen using a roll of tape to seal the flaps of a cardboard box. The person starts by placing the roll of tape on the edge of the box's flap and then proceeds to tear off a piece of tape. They then fold the tape over the edge of the box and press it down to secure it in place. The person repeats this process on the other side of the box to ensure that both flaps are securely closed. The video provides a clear demonstration of how to properly seal a cardboard box using tape.