I was wondering if its worth buying or not,so i'm curious about a bunch of things:

How does the gambit system work?
Is it true that FFXII plays like an online game?
IS it true that you can make the game practically play itself?
How much is there to do in FFXII?

Yes, it's worth it.

Gambits: In your party you'll have 3 or 4 character but can only control 1 at a time. Gambits are basically instructions you can program for the AI so you can control how it behaves. It's very easy to use and very useful. You'll understand it better once you try it out.

No, it doesn't really play like an online game. There are some elements that feel MMO-ish, but not in a bad way.

Making the game play itself, is done with the gambits, in a way. If you set gambit for every character properly you can make them react to most situations effectively without much input from you. Essentially, making the game play itself. However, if you just leave it on auto-pilot all the time, you WILL die, no matter what kind of gambits you've set. So don't worry about that too much. You'll still actively participate in combat.

A FREAKING LOT. Personally, speaking I've spent 300+ hours in this game.

1:I saw in FFXII,that you can move around the map,but there was a weird arrow thing.I thought FFXII limited how far you could move when you hit things?

2:I saw also,that its a lot less turn based,and more real time than FFXIII.
3:How does the weapon upgrade system work in this game? And is it really that open? I saw a guy in an FFX video leave a town and just go around attacking things,looking for a tomato alien thing.
4:is it true,that there are many parts that go nowhere in the story? I hear a lot of bad stuff about FFXII story.

Story isn't what I'd call bad per se, but it's very unorganized. It feels like an afterthought, it definitely isn't the high point, imo.
Yes, it is in real-time, but not completely, I can't really elaborate any more than that, you'd have to play it to find out. It's a bit complicated, but you get used to it.
There is no weapon upgrade system. You just swap your equipment for better ones you find in your travels.
Not sure what you mean with the arrow thing.

I saw a lets play,and there was an arrow guide on top of the enemies head in a dungeon of sorts.There were a bunch of characters hitting an enemy.

The real time battles actually look kinda interesting in FFXII.

Yes, it's most definitely worth the money. The story is kind of scattered, as Smarty said, but the combat system is nothing short of excellent. It's not without its share of flaws, but it's very enjoyable. Most of the flaws in my opinion come from the fact that the story consists of "Go to this plain, now go through this cave, now go to this town, walk around, leave, go to this plain, go to this dungeon..." It's pretty repetitive, what with the nondescript locations and numerous palette-swapped enemies. That being said, I still think it's great. I think that what this game does right outweighs what it does wrong. And it's only like $11 nowadays, and for 300+ hours plus replay value, I'd say it's damn worth it.

I'm going to have to pirate it some day,just to test it out.

If i like it,then maybe i'l buy it.