1) What does he mean this does contain "hackivation!" Hacktivation is a process that activates your phone (fake activates) instead of having to contact the AT&T server. Basically this is for people who do not have a legitimate iPhone plan with AT&T, so T-Mobile users etc..
2) When i unlock the iPhone 3Gs 3.1.2 do i need to have a sim card in it? Yes you need a sim card to unlock. I'm not 110% sure, but I am pretty sure you need to have a SIM of some kind in the phone for the process to work.
3) If i DONT need the Sim card, Can the Unlock stays Unlocked till when ever i put my sim card? For software unlocks, the phone will stay unlocked until you restore it. But again, I'm pretty sure you need a SIM in the phone.
4) If i Restore the iPhone the Unlock Disapears? and i have to re-unlock it again? Unfortunately yes, software unlocks will be to be re-unlocked.
5) If i updated to a newer version Im Screwed? By meaning no way to Downgrade. ( I WONT update just to be stupid but im curious what would happen) You can most certainly downgrade firmware on an iphone, but the problem comes in if Apple decides to change the baseband, as they did with 3.1.x from 3.0.x - the newer baseband was not unlockable until now, so anyone who upgraded to 3.1.x firmware lost their unlock. You can always downgrade, but the baseband is not downgradeable and that is what causes the problems. Also, downgrading can sometimes screw with your baseband (modem firmware) and your phone can be rendered useless. I've seen this before. But yes, you can upgrade and downgrade at will but the baseband/unlock is an issue. For instance, I only jailbreak, I do not need to unlock as I have AT&T, so I could upgrade/downgrade and probably not have issues as I don't need an unlock, but someone who needs to unlock would be screwed as they can not downgrade their baseband (at least not right now).
6) When i Unlock does anything change inside the iPhone? what do you mean by "inside" the iPhone? Hardware wise? No. It does not physically change anything. All it does is trick the phone into letting you use it on other carriers. It will alter files, yes.
7) What if i want to get rid of my jailbreak and keep just unlock? how do i do that. You can't. Point blank.
Edit: 8) What does Bricked means? i hear it often here. Bricked means the phone does not function. When you brick your phone it means it becomes unresponsive. Most of the time a bricked iPhone can be fixed by forcing it into DFU mode and restoring it. I have also seen people brick an iPhone more extensively to where iTunes does not want to recognize it, then you have to force restore it. I've only ever had this happen once to me and I found a fix through using the Terminal on my Mac. but like I said 99.9% of the time, a bricked iPhone is never FUBAR.
Most of the questions you had here have pretty much already been answered or a simple google search probably would have answered most, if not all of them. But I hope this helps and gives you some answers.