When I jailbreak my iPhone 4 running 4.3.4 it crashes and when I use any app it doesn't work. Why ?
Well first of all jailbreaking is illegal . So, just don't do it. Plus it makes the phone really slow. So slow that I would rather spend like a 1000 bucks just to buy the apps.
Because there isn't a jailbreak out yet for 4.3.4 so it doesnt work
The jailbreaks for 4.3.4 are not good, try downgrading to 4.3.3 if you can, then jailbreak it so easy just by going to jailbreakme.com on your device and on cydia find app sync and install it. Your device is good to go.