Don't be surprised if it's old intro and outro, this walkthrough is one of the old ones I did and never uploaded until now, so yeah, enjoy ^^
Link : https://www.moddb.com/mods/brave-brain
You play as Thomas Redgrave, a friend of Gordon Freeman, who works in different laboratories of Black Mesa on the same day of the accident.
You are taking a refresher training course when things go wrong. Do your best to survive until you meet some other scientists, who tell you exactly what you need to do.