Go downstairs and save. Talk to Tifa. You will switch back to controlling Aeris so try to go out the front door, to find you’re surrounded. You will talk for a while, then watch the kick-ass FMV. Afterwards you’ll play a mini-game in which Cloud must protect the van by swiping the oncoming motorbikes with his sword. Press Square to attack left and O to attack right. Before starting, form your party and equip yourself with Bolt, Ice and Cure/All materia. During the mini-game there is a gauge showing how much health everyone has, as the van gets attacked their HP will go down. At the end of the mini-game you’ll fight at large machine boss…
This boss with get the first attack from behind, but if at the start of the battle you hold L1 and R1 as if trying to escape you will turn around at the back attack won’t be a back attack any more so you will take less damage. Also your characters will only have as much health as they had left after being attacked in the mini-game. If a character was killed in the mini-game they will start this battle with 1 HP, and as the boss gets the first attack, they will need to be revived. Use Bolt and Ice on the boss, and be careful of it’s flame attacks (Twin Burner) if you are at a low level, so have someone with Cure/All to heal your party.
After the battle, your characters will talk for a while, you’ll find yourself at a screen you could have seen but not accessed if you went south from Aeris’s church. Talk to everyone here and go south to enter the world map. You can now save anywhere on the World Map. You can either fight around here to level up, which I suggest or go straight to Kalm. Head east from Midgar and you should see a town nearby. Enter. You can buy materia, weapons and items here. When your done, go into the inn.