How?

[kcoppock]

You want them to come out grainy? That's usually (not always) the opposite of what people want. I would rather add grain in post-processing and have a clear original. That said, just raise your ISO, it will introduce more noise into the image the higher you go.

To take night photos like you're talking about, you should definitely get a good, sturdy tripod. For including people and a dark background (such as the fireworks example you mentioned), you should also look into getting a good flash and diffuser and practice using Slow or Rear Sync flash methods.

[Hill Country Hack]

I posted this Christmas Lights yesterday. This may get you started with what you asked about. A tripod is a must with the slower shutter speeds. As earlier mentioned a cable or wireless release is nice to have. Look in your manual and find out how to do "mirror lockup" as this will lessen camera shake and use the auto timer so you are not touching the camera when the shutter releases.