Use //set cobblestone.
no
you have to cyt
Single player commands are needed.
You get a mod, such a Single Player Commands.
well minecraft 1.2.3 single player is beta so there are no commands hopefully in the next version
you can install Single Player Commands and there is a freecam option.
A single piece of coal can perform 8 furnace operations in minecraft 1.6, so that means 8 pieces of cobblestone.
do /clear inventory or just /clear
In multiplayer, commands are generally started with a "/" Single player commands have not yet been added, unless you get a mod that has commands, like WorldEdit. They will be added in the next update, 1.3.
Try a mod. You could use InvEdit or SPC (Single Player Commands).
Have you installed ModLoader and/or deleted the META-INF folder in the minecraft.jar.
Get single player commands then type in spawn silver fish. Make sure it's not on peaceful.