The Stronghold and the End

An eye of ender is crafted from an ender pearl (dropped by killing endermen) and blaze powder (crafted from a blaze rod, itself only available from Nether fortress blazes). Thrown into the air, it drifts in the direction of the nearest stronghold before dropping, and sometimes breaking instead of landing safely. Repeating this, walking toward wherever it lands each time, guides you to a stronghold buried underground. Once an eye starts dropping nearly straight down instead of drifting sideways, you're right on top of it, and it's time to start digging.

A stronghold's portal room holds 12 end portal frame blocks arranged in a 3x3 square shape with the four corners left empty. Each of those 12 frames has roughly a 10% independent chance of already holding an eye of ender when you find it, so a handful are commonly already filled, though it's entirely possible to find one with none. Fill every remaining empty frame with an eye of ender and the center fills in with a swirling black-and-purple void, the activated End portal. It's worth bringing a few spare eyes beyond the twelve you might need, since each throw carries a real chance of breaking instead of placing.

Stepping through the activated portal drops you straight into the fight with the Ender Dragon. The dragon roams among tall obsidian pillars, each topped with an end crystal (two or three of which are protected inside iron bar cages) that continuously heals the dragon back up whenever it flies close. Attacking the dragon directly while those crystals still stand is largely wasted effort, since the healing easily outpaces the damage most players can land. Destroying every crystal first, usually by shooting them from a distance, is what actually lets a fight against the dragon's health make real progress. Once the dragon is defeated, a portal called an End gateway opens nearby, leading to the scattered outer islands of the End, where End cities, tall structures built from purpur blocks, sometimes hold an End ship carrying the one item that makes exploring those islands far easier: elytra, for gliding.