Take the gravity gun from the robot's hand ( #1) and wait for the girl to finish talking. When they go up, use your gun to get rid of the planks holding the metal gate ( #2 ). When it falls, it will create a bridge that will let you to join the rest of the company. Alyx will contact her father and doctor Kleiner.
Chapter 1: To the White Forest 4. Along the left wall near the remains of the antlions is an alcove with more shotgun ammo, some grenades, and a poorly covered pit. Uncover the pit with the Grav LNurX.