First you need to find the .minecraft file.
If you're using Windows 7 or vista, open the start menu on the bottom left and type in "run" on the search field, and you'll open a little window. Here, type in %appdata%/.minecraft
If you're using a Mac, the .minecraft folder is here: [computer username]/Library/Application Support/minecraft
If you're using Linux, the .minecraft folder is here: /home/[computer username]/.minecraft
Here it will be a folder named bin, which you have to delete. The bin folder is basically all updates and everything that has been added after you downloaded the game. When you delete this folder, you'll also delete all the updates, so when you start Minecraft again, you'll have to install all updates again.
It depends - a mod for what exactly?
The how-to depends on the game and the machine you're playing on (PC, PS3, Xbox, etc).
Re-ask the question with the missing information.
Maybe because you have a mod that won't let you. You should get rid of that mod.
It probably won't work and you'd have to get rid of the mod and try and find a more updated one. It probably will work though.
Minecraft doesn't have an official best mod.
Nope. You HAVE to download a minecraft mod to have it.
a mod where you can fly a plane on minecraft so get it
Mo Creatures is a modification (mod) for Minecraft. You can get this mod by downloading it from The Minecraft Forums.
One example of a superhero mod in Minecraft is Superheros Unlimited for version 1.6.4.
Just search in google 'Minecraft mod downloader'
You can get a mod to do just about ANYthing you want, just do a Yahoo/Google search for something like "minecraft mod".
The Ender Dragon is a part of Minecraft, not a mod. You probably need to update Minecraft.
You can mod minecraft in the mac.
In minecraft beta, there is creative mod what allows you to get all items.