As a first step you will need to make sure you have a java compiler installed and, not necessary but very useful, a good java IDE such as Eclipse.
Next you will need to decide if you are going to mod against the minecraft code using MCP (Minecraft Coders Pack) and SMP ModLoader; or Bukkit or Canary. Modding against Minecraft gives you the ultimate flexibility, but at the cost of potentially making it so that your mod is incompatible with other mods. Also, using the modding API provided by Bukkit or Canary is a lot simpler than trying to understand the minecraft code, especially if you are just starting out with modding.
After selecting which method you will be using read up on the API and tutorials that the site provides and if you have any questions or can't figure something out, ask in the respective forum, chances are someone can help you.
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no it only works on singleplayer beacuse it is a mod in a village and not online.
There is no cider in Minecraft unless you have a mod.
Mod
You have to have a mod (modification) to make a cannon. It is not in vanilla minecraft.
you can't make a pencil in minecraft, but there mite be a mod for it.