Craft a crossbow using 3 sticks, 2 string, 1 iron ingot, and 1 tripwire hook
Craft fireworks using 1 paper and 1 gunpowder
Open the crossbow in your hotbar
Put the fireworks in your off-hand or inventory
Load the crossbow by holding right-click or the use button
Fire the loaded crossbow to launch the firework rocket
Use multiple gunpowder in the firework recipe for longer flight time
Do not add a firework star if you want a basic launcher rocket