There is no way to spawn Herobrine in Minecraft, since he is just an urban legend, and does not exist in the game.  However, there are mods which allow you to summon Herobrine.  Many of these mods require you to ignite netherrack on an altar made of gold and torches.  Doing this will summon a mob which acts like how Herobrine is described, placing traps for the player and messing with the world.
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