Throw an Eye of Ender (right-click) and it will fly in the direction of the nearest Stronghold. Follow it until it starts flying downwards, indicating the Stronghold is beneath you. Dig down carefully. Inside the Stronghold, find the End Portal room. Place the remaining Eyes of Ender into the portal frames to activate it.
Minecraft
Locating and Activating the End Portal
Locate Minecraft's rarest structure by throwing Eyes of Ender and following their trajectory to find the Stronghold and activate the End Portal.