Can someone explain how meteor was created again? Because in that super super super super long story line before that, I was sort of in a hurry and didn't it well. Can someone explain?

Meteor is simply a collection of spacial rocks and debris. The spell itself just pulls them all into one small area - thus forming what we see being Meteor.

Did this same cutscene show the way meteor was created?

I thought it was disk 1...

The pic shows how Sephiroth summoned meteor. Which I suppose is a yes to how it was created. Sephiroth used the power of this black materia to bring forth meteor from space.

I think there's an explanation regarding the summoning of Meteor at the Temple of the Ancients... at the very least I remember there being glyphs and figures on the wall representing the power of the black materia (i.e. the power to call Meteor).

^ More like nukes strapped to his chest.

Anyway, I think that Meteor can be cast just like any other spell. The only difference being that in order to use the Black Materia you'll need to be powerfully adept in magic, which defines Sephiroth pretty well.

As for the formation of the Meteor itself, it's probably just like what Saix said:

Or the spell could easily locate the nearest asteroid and pull it towards the Planet.