Don’t stress it if things aren’t going well at the fireworks display.
Put the camera on the tripod. Frame the scene in front of you. Set the camera’s mode to Aperture Priority. Dial the f/stop to 5.6. Raise the ISO to around 400.
Take a couple of shots. Look at them on the back of the camera. Too bright, then drop the ISO to 200 or 100. Not bright enough, raise the ISO to 800 — though this is usually not the case. Take a couple of shots and repeat.
The key is to not get flustered. You can do it!