I have no clue on how you add a command to Minecraft. The commands like /help, /clear, /kill if you're wondering.

for 1 you need to make a command class, here is a premade one from minecraft

Give Command

 

 

package net.minecraft.command;

 

import java.util.List;

import net.minecraft.entity.item.EntityItem;

import net.minecraft.entity.player.EntityPlayerMP;

import net.minecraft.item.Item;

import net.minecraft.item.ItemStack;

import net.minecraft.server.MinecraftServer;

 

public class CommandGive extends CommandBase

{

    public String getCommandName()

    {

        return "give";

    }

 

    /**

    * Return the required permission level for this command.

    */

    public int getRequiredPermissionLevel()

    {

        return 2;

    }

 

    public String getCommandUsage(ICommandSender par1ICommandSender)

    {

        return par1ICommandSender.translateString("commands.give.usage", new Object[0]);

    }

 

    public void processCommand(ICommandSender par1ICommandSender, String[] par2ArrayOfStr)

    {

        if (par2ArrayOfStr.length >= 2)

        {

            EntityPlayerMP var3 = func_82359_c(par1ICommandSender, par2ArrayOfStr[0]);

            int var4 = parseIntWithMin(par1ICommandSender, par2ArrayOfStr[1], 1);

            int var5 = 1;

            int var6 = 0;

 

            if (Item.itemsList[var4] == null)

            {

                throw new NumberInvalidException("commands.give.notFound", new Object[] {Integer.valueOf(var4)});

            }

            else

            {

                if (par2ArrayOfStr.length >= 3)

                {

                    var5 = parseIntBounded(par1ICommandSender, par2ArrayOfStr[2], 1, 64);

                }

 

                if (par2ArrayOfStr.length >= 4)

                {

                    var6 = parseInt(par1ICommandSender, par2ArrayOfStr[3]);

                }

 

                ItemStack var7 = new ItemStack(var4, var5, var6);

                EntityItem var8 = var3.dropPlayerItem(var7);

                var8.delayBeforeCanPickup = 0;

                notifyAdmins(par1ICommandSender, "commands.give.success", new Object[] {Item.itemsList[var4].func_77653_i(var7), Integer.valueOf(var4), Integer.valueOf(var5), var3.getEntityName()});

            }

        }

        else

        {

            throw new WrongUsageException("commands.give.usage", new Object[0]);

        }

    }

 

    /**

    * Adds the strings available in this command to the given list of tab completion options.

    */

    public List addTabCompletionOptions(ICommandSender par1ICommandSender, String[] par2ArrayOfStr)

    {

        return par2ArrayOfStr.length == 1 ? getListOfStringsMatchingLastWord(par2ArrayOfStr, this.getPlayers()) : null;

    }

 

    protected String[] getPlayers()

    {

        return MinecraftServer.getServer().getAllUsernames();

    }

 

    /**

    * Return whether the specified command parameter index is a username parameter.

    */

    public boolean isUsernameIndex(int par1)

    {

        return par1 == 0;

    }

}

 

 

Then in your main class you must put

ModLoader.addCommand(CommandClassHere);