The introduction gets right into the action. At the very beginning, you're controlling an ex-SOLDIER, now employed by AVALANCHE, and you learn to use the combat interface. The first few military police (MPs) are not too difficult to deal with; just hit them with regular attacks. Final Fantasy VII's manual booklet gives a lot of interesting tidbits on how to fight, but it isn't very difficult. Choose "Attack" and then the bad guy, and after a few hits the enemy dies. Although you can use materia at this point, it is wasted on the soldiers as they are very weak, so you are better off just holding the button, which will cause the game to automatically select and attack the nearest target.
Notice that if you hit during battle, you can see the name of the enemies that you're attacking.After you've defeated the guards, there is a brief introduction to the game; walk up to the fallen guards and hit to examine the bodies of the two guards to scavenge a potion from each. Hold while moving to run, which will speed the game up for you considerably.
Turn right, then left, following Biggs. Go through the door to the bridge, then turn right with the others.Now you're in the reactor. Talk to Barret, and he joins your party. Talk to Biggs, then Jessie. Once you're in the elevator, go in front of the triangle shaped buttons, and press .
Follow Jessie out of the elevator, and down the long stairwell on the side. You need to go all the way down until you're on solid ground. If you lose track, press Assist () to get a cursor above your head.
You'll see a shiny blue object in the area with the golden metal poles. Pick up the Potion, then continue on down the ladders. Jessie will stay put. Keep going over a large pipe and you'll see the first save point after a moment. Continue down the long bridge pathway. Pick up the Restore materia, then check your party's HP and use a tent if it is very low, as you will have your first boss fight in a couple seconds, then go to the gold-colored wheel. Cloud gets a weird vision then the fight begins.
The boss leaves an Assault Gun, which Barret can use, and is better than his default weapon so equip it. The time bomb is set, and you now have 10 minutes to go back the same way you came. Along the way, you'll run into Jessie, whose foot seems to be stuck. Talk to her and help her to get loose again. If you missed her and get back to the rest of the gang, you still probably have plenty of time to get back and there again. Once you're out, the reactor blows up.
Train to Sector 7
After you escape, you and the rest of AVALANCHE split up. There isn't much to see here, but you actually do get to meet Aeris for the first time. You don't know her, but she's going to be a really important character later on. You can buy flowers from her if you want to (you can use them in the story later). There is a Potion lying on the ground just before the south exit in this area.
When you finally head towards the train station, you get surrounded by soldiers, who, as the beginning of the adventure has shown, are quite trivial to defeat. You can actually choose to avoid fighting them, but it's probably best to fight them for additional experience and items. Eventually, the fight ends, and you leap from the bridge to the roof of the passing train, conveniently right on the correct car too.
There isn't terribly much to do aboard the train, just talk to the AVALANCHE members as you see fit. Jessie will show you a computer diagram of the railway system. After you get back to the station, head left, where you find, among other things, a save point. The Sector 7 slums are further to the left.