Do you mean you want to be able to open the camera without having to enter your password? I'm not sure you can do that without disabling the security lock.
If that's not what you meant and you don't already have it, you can add a camera shortcut to your lockscreen by going to Settings > Lock Screen > Lock Screen Options and then press the 'Shortcuts' option at the top (not the slider, although that should obviously be turned on). You should then be able to add/change the shortcuts available on your lockscreen.
