How do you make mobs spawn in minecraft?

Answer 1

Chickens, cows, sheep, wolves, and pigs will spawn on well lit grass in the Overworld. (Not the nether or the end.) Mooshrooms will spawn on Mycelium in the Overworld, Skeletons, creepers, Spiders, bats, and Zombies spawn in dark places. (Only in the Overworld.) Zombie pigmen and ghasts spawn randomly in the nether. Skeletons, and wither skeletons spawn in nether fortresses, and blazes spawn only near blaze spawners. (Found in nether fortresses.) Ocelots spawn in jungles, and squids spawn underwater in the Overworld. Endermen spawn rarely in dark places in the Overworld, or witha much higher frequency in the end. Cave spiders spawn from spawners found in abondoned mineshafts. Villagers spawn when the map is created and when other villagers breed and have babies. Slimes spawn at low elevations in slime chunks or in swamps. Silverfish spawn from their spawners in one of the worlds three(or less) strongholds. Witches spawn in witch huts when the map is created. One ender dragon spawns in the end when the map is generated. Those are all the mobs which are created naturally, for more information, I advise you go tohttp://www.minecraftwiki.net/wiki/MobsIf all these conditions are fulfilled, and no mobs are spawning, I suggest you press Esc and change your difficulty to easy, medium, or hard, as no monsters spawn while you are in peaceful mode.

In creative mode you can also use Spawner Eggs (found in your inventory) to spawn mobs