You go into your creative inventory, scroll all the way down, then select the egg of the mob you want to spawn, then put it in your hot bar, select it, and right click on any block surface to spawn the mob.
In Minecraft Classic, mobs can't spawn, so they can't exist naturally. If you play the Survival Test, and when mobs spawn there, you can save it and open it in creative mode so then the mobs can stay there. However, in Minecraft Creative Mode, mobs can spawn, but they can't hurt you because you have no healthbar.
If the difficulty isn't set to peaceful, mobs will spawn in creative mode.
In creative mode you can spawn a zombie with the egg
spawn it with an ocelot egg
You can only spawn mobs in creative mode, where they give you spawn eggs. if you use a squid spawn egg in water, a squid should appear.
You can't. There are two Minecraft demos that I know of: one on minecraft.net, and the PC Gamer demo. Both are locked in survival mode, and in survival mode there is no way to spawn mobs.
There are no hostile mobs in Peaceful difficulty mode on Minecraft. Mobs such as creepers, skeletons, zombies, spiders and all other manner of hostile mobs do not spawn while Peaceful mode is active, though you will see (in dark places or at night) mobs attempting to spawn and immediately disappearing a millisecond after appearing. Mobs cannot attack you regardless unless another difficulty is triggered.
Yes you can. You could also spawn them in using the spawn eggs.
You may have your difficulty set to Peaceful. Monsters will not spawn in Peaceful mode.
You can't, they are only spawned naturally. You can, however, use a spawn egg in creative mode to spawn them.
There is no button to spawn eggs in minecraft, unless you are in creative mode in which case you press the Inventory button. Creative mode can be made to happen when you create a creative world or install a mod that lets you switch gamemodes ingame.
By either going into creative mode and getting a Spawn Egg, or by activating "Cheats" in Survival mode and using the command "/give (Minecraft Name) (Number) (ID Number for Spawn Egg/Name of Spawn Egg)"