I have a D5300 and it is a LOT of camera if you are new to digital photography. Do yourself a BIG favor and pick up "David Busch's Nikon D5300 Guide to Digital SLR Photography" for about $25 at any major bookstore chain. It expands nicely with colorful examples upon things the camera manual doesn't explain well.
If you are in a real hurry to take decent photos, just leave it in program mode and you should be okay. On the top dial there is a "no flash" setting - learn where this is at, otherwise it will keep popping the flash up when it gets dark, under-exposing your pic. The sunset/landscape/sports/etc settings are simply presets that are optimized for those conditions. For storm photos I generally avoid using them.
Issues you will run into as a beginner with this camera:
1. Autofocus has problems finding focus on non-contrasty things like clouds. You might want to flip your lens over to manual and focus it yourself.
2. Depending on your settings, your lens will try to constantly focus during video. This is very annoying and unnecessary for storm photography, and often you can hear the AF motor hunting in your audio when you play it back. Again, flip your lens over to manual and focus it yourself. For the most part, you only need to focus on a storm once and subsequent pics/video will be in focus.
3. The camera will try to use the flash when it is dark unless you specifically tell it not to. You can't use a flash against something further than about 50 feet away, much less illuminate a whole storm system from miles away. Compensate by using as large an aperture as possible (large aperture = smaller "f" number, like 4.0 or 5.6), and increase your ISO setting.
Practice taking pics of regular clouds on non-chase days so you can see how your camera acts - that way you will know what to expect and spend less time fiddling with settings and scrolling through menus when that awesome wall cloud is in front of you.
Buy that Busch book - it is very helpful.
TR
TR