Open a crafting table
Place 1 paper in any crafting slot
Place 1 to 3 gunpowder in any crafting slot
Craft the firework rocket
Add 1 firework star to the recipe if you want an explosion effect
Use up to 3 gunpowder to increase flight duration
Combine the rocket with dyes, glowstone dust, diamond, fire charge, feather, gold nugget, skull, or creeper head through the firework star to change explosion effects
Use the crafted firework rocket in your hand to launch it