For changing the shutter speed you simply just scroll the wheel on the back of the camera which should make the numbers on the left change that is your shutter, the numbers after the F on the right would be your F stop (which is changed by scrolling the same wheel while holding the +/- button at the top right of the camera) ,scrolling to the right for shutter gives you a quicker shutter scrolling to the left give you a slower shutter so you can adjust accordingly. (Nikon is backwards from other cameras) Long time exposures dealing with seconds and up you want to scroll left until you get to numbers that end in " that indicates seconds 2" would be 2 seconds 1.6" would be 1.6 seconds 20" would be 20 seconds and so on. If you scroll all the way left past 30" you'll reach a mode called bulb, this is infinite long time exposure, you have to hold down the button to take the photo but it takes until you let go, or if you have a remote like me you simply trigger your camera and trigger again when you want your exposure to end.

Lightning is a bit trick but if you want to learn i say get the basics of your camera down (things like shutter speed,iso,f stop and such) and try these tips

How To Photograph Lightning

Hope this clears thing up