It's quite easy. First of all, you need to head into Settings, then on the top you should see My Device. Choose that and you will be taken to a different category of settings.
Now from there, look for Lock screen. After that, make sure to check the box where it says Multiple widgets, then head to the option under it called Lock screen widgets.
From switch the first option to on which says Favorite apps or camera, then you should be taken to another menu and you should see Camera as the last option. Choose that and you are done.
Now to access your camera shortcut while your phone is locked, simply press the lock button and once the screen lights up, drag to the right and you should see a huge box with a camera icon inside it.