BeginnerExploration
How to find the End portal (stronghold) in Minecraft
Wear full armor and bring a sword, food and a Bow or Crossbow with plenty of arrows for the End Crystals.
Tested 26.3
An End Crystal is a floating crystal that heals the Ender Dragon and explodes when hit.
It is made with the Crafting Table from Eye of Ender, 7 × Glass and Ghast Tear.
What it does
Crystals on top of the obsidian pillars heal the dragon, so destroy them first. Craft one from seven glass, an Eye of Ender and a Ghast Tear; it can only be placed on obsidian or bedrock. Four crystals on the edges of the exit portal summon the dragon again.
How to craft
Crafting table 
7 × Glass + Eye of Ender + Ghast Tear → End Crystal
// Slots with several items cycle through every accepted option.
Tutorials with End Crystal (1)
End Crystal · FAQ
How do you get End Crystal in Minecraft?
At the Crafting Table: 1 × Eye of Ender, 7 × Glass and 1 × Ghast Tear give 1 × End Crystal.
What is End Crystal used for in Minecraft?
It explodes when hit and respawns the Ender Dragon.