Just read the "complete jailbreak guide" at the top of the iPhone, iPad, iPod section of the forums, try the things their and don't forget to make sure your baseband can be unlocked, and figure out the production date of your 3GS as after week 35 or 45 of 2011 apple got toshiba to make some price of hardware for 3gs's and they can't be unlocked yet. If you are unsure about any of it then don't do it coz u can totally screw up ya phone.