So I've google searched and whatever. I'm a huge noob at this, just trying it for the first time and I was able to successfully jailbreak it with redsn0w, the tethered way. Greenpois0n wouldn't let me do it, everytime I attempted, it gave me the...Failed 
but redsnow allowed me to do it.
Oh I have an iphone 3gs with 4.2.1 and uhh not sure what baseband...but if it's the modem firmware its 5.15.04.
So basically look: I am able to jailbreak it successfully with redsn0w and get cydia but the thing is, after adding all the updates and stuff and then rebooting it, I go to download all the fun apps that I assume is the whole reason we jailbreak it and then I have to reboot the phone again but it doesn't like...start up again, it just stays stuck on the pineapple screen(the jailbreak reboot screen?) and then after a while the phone like retries to boot up normally with the apple icon and it doesn't work either. What the hell am I doing wrong and is there a way to get this phone jailbroken and working!?
but redsnow allowed me to do it. Oh I have an iphone 3gs with 4.2.1 and uhh not sure what baseband...but if it's the modem firmware its 5.15.04.
So basically look: I am able to jailbreak it successfully with redsn0w and get cydia but the thing is, after adding all the updates and stuff and then rebooting it, I go to download all the fun apps that I assume is the whole reason we jailbreak it and then I have to reboot the phone again but it doesn't like...start up again, it just stays stuck on the pineapple screen(the jailbreak reboot screen?) and then after a while the phone like retries to boot up normally with the apple icon and it doesn't work either. What the hell am I doing wrong and is there a way to get this phone jailbroken and working!?