-Right after getting out of the tram and the guard is having trouble opening the door, turn around. Eventually, another tram will pass by with Gordon Freeman inside it, which is the start of Half-Life.
-After you finally get in the locked door at the start, find the strips on the walls which will lead you to different areas such as the armory and personal facilities. Find the one which reads "Video Surveillance". Follow it to a security room which will have monitors. Go up to each one of the monitors and press "Use". One should show the shooting range and another will show a female in a hazard suit pushing a cart. However, one of the monitors will show Freeman arriving at the Anomalous Materials lab. He will walk past another scientist, who will say "Good morning Gordon".