You’ll now control Tifa and after she freaks out, you’ll be in a place of Cloud’s memories. Firstly talk to the Cloud in the north, when Nibelhiem is. Go north a bit, and then talk to Cloud when he appears. When your back with the other Cloud’s talk to the one on the left, looking at the well. After that’s done, talk to the Cloud on the steps, then to the kid Cloud. After Tifa and Cloud fall, talk to the shadow of Cloud. Then follow Cloud to where Niblehiem is and talk to him. Then go into Nibelhiem. You’ll go to the Mako reactor. The rest of the story should unfold and you’ll learn who Cloud really is. After that, talk to Cloud one last time and you’ll be returned to the real world.
When you have returned to the Highwind, talk to the guy here and make a new team. You might want to go back to Mideel and buy some more things from the hyper kid up the slope. Also go to the Chocobo Farm and buy some Mimett Greens and give them to the white chocobo (they are called Salerno Greens there for some reason) and you’ll get the Contain materia. You might also want to spend this time breeding chocobos before going on with the story, as you can get the Knights Of The Round materia which can wipe out the rest of the bosses in one hit. You can also go into the Gold Saucer again, and get the key to Midgar from the Bone Village (see Tifa’s Ultimate Weapon). Anyway when you are done, go to Junon.