The default setting for digital zoom is OFF.
If you have not turned it ON, it is already OFF.
You turn it off/on by a setting in the Menu.
If you look at the index in the Instructions Manual, probably under "Advanced Recording" you should find Digital Zoom.

Digital zoom degrades the quality of the photo.
Somewhere in time, someone thought digital zoom was a good idea. Anything digital zoom does, can also be done with software. Software does it better.

The LCD will see just about anything your eyes can. If it is too dark for your eyes, it is too dark for the LCD.

If you are trying to take a picture of the moon at 12X and you are hand holding the camera, it only takes a slight movement to completly loose the moon in the LCD. First look at the scene at no zoom, then add a little zoom, and continue to add zoom and notice that the more you zoom, the more the moon jumps around. For that type of shot you should use a tripod.

For fireworks shots, I have never seen a fireworks show that needs any more that 3X of zoom.

I don't know of any site that does a step-by-step on any particular camera.