Are you creative? No? Well, you can use your creativity in Creative Mode! When you create a new world, select Creative Mode. In creative mode, you have access to every single thing! Just open your inventory. You can pick blocks and build!
Build build build build build build- Oh no! You made your house out of TNT and it blew up when you pressed the button to open the door!
That would be bad. It would be baaaad if there was a sheep, too.
Yes, Creative Mode is that simple.
If you have cheats active, there are plenty of commands. Just type / in chat and the command after it. I will only cover a few.
/gamemode: Type /gamemode c for creative, /gamemode s for survival, and /gamemode a for adventure mode. In adventure mode, you can't break or place anything.
/tp: @p means nearest player, @a means all players, @s means you, @e means all entities. Or you could type the player name instead of @e to just affect that player. Example: /tp Minnow2009 350 71 -30 will teleport Minnow2009 to coordinates 350, 71, -30.
/kill: Type /kill @a to kill all players, /kill @e to kill all entities, /kill @s to commit suicide, and /kill @p to kill the nearest player. Or their name to kill that person. Example: /kill Minnow2009. (I'm not sure why you'd want to kill me, but whatever.)
Have fun in Creative Mode!
fun