Let's talk about the TV setting today. TV stands for Time Value. I believe for a Nikon it is called S for Shutter Priority. When you put your camera in TV you are setting the shutter speed. The camera will set the aperture for you.
Shutter Speed is how fast your lens opens and closes. If you want your pictures to be crisp and sharp you need to have a high enough shutter speed to freeze the movement. Usually a setting of 100 or 200 is pretty good. I only use TV setting when I am trying to get artsy with photos. Either, I'm trying to catch motion such as jumping like this:
My TV for this photo was probably over 2000. I wanted to freeze the movement in my picture.
For this photo, I set my shutter really slow. I wanted the movement to show in the photo.
When you set your shutter speed really slow, you need to hold really still or use a tripod. If you shake, it will show up in your photos and your subject will be blurry.
When you shoot fireworks, you can set your shutter as slow as it will go. Sometimes your camera will show the word "bulb" when you do this. That means your shutter will stay open until you close it. So you will push the shutter release (the button) expose the photo for as long as you want and push the shutter release button again. I took these pics with a tripod and just set my shutter to expose for about thirty seconds.