This guide is a simplified overview of all the changes in the Exploration Update (Java Edition 1.11.x releases), which assumes at least some familiarity with the Frostburn Update (Java Edition 1.10.x releases).
While flying using elytra, using a firework will give the player a boost for a certain amount of time. This will emit particles when in use.
Fireworks stay at the players location until they disappear or explode.
Longer flight duration on the rocket will make the boost last longer. You can increase the flight duration of a firework by crafting it with gunpowder in the other slots.
Fireworks with an explosion will deal damage at the end of their flight.
Firework explosions now hurt surrounding mobs and players.
The damage radius of the explosion is about 2-3 blocks and is the same for any shape (large ball, creeper, burst, etc.) and the damage decreases with the distance to the explosion.
The damage amount at close range is about 5 without armor on, and with full diamond armor, it equates to about 1.
When in crosshair mode, the weapon is fully cooled, and a mob or entity is in range of attack, the attack indicator will be visible and will include a small plus sign (+) underneath the crosshair.