1st thing get a tripod, no tripod, not worth shooting for me.
Once u have a tripod, (if you have no add ons or remote and just shooting frm the camera), make it to self timer mode , high f (f15- f22 etc) and shutter speed 30 secs to make "paint" the picture.
Oh and camera cant focus in the sky because there is no contrast there, so switch to manual focusing and put it to the middle of the infinity sympol. you will see the number 8 lying down.
You MUST include landscape filling up maximum of 1/8 at the bottom of the picture to show the "size" of the fireworks, if not the picture woukld be of no sense