How do I backup my MineCraft world?

Automatic Solution:
Obtain a version of MineBack and follow the guide below.
Manual Solution:
To perform a manual World backup, copy the entire content folder
<World Name>
 into a safe place.
This guide will take you through making backups using MineBack Ultimate, when you first launch MineBack it will search for your saved worlds. It will automatically locate them and will show a screen similar to the following:
Backing up using MineBack Ultimate

If you simply leave MineBack unconfigured and running like this (with the Automatic Backup checkbox ticked) MineBack will automatically manage your world backups intelligently as you play MineCraft!

However, MineBack can't always know your intentions so its sometimes best to make a explicit automatic backup before beginning play. This is very simple to do, simply click on the world you wish to backup (from the top half of the MineBack screen) then click on the Backup button (shown in green). That it! If you want to differentiate the backup your making, type in a name in the Backup Description Personalisation box.

Restoration is just as simple! Simply select the world you wish to be restored and the lower half of the window will show a list of dated backups, click on the backup you want to go back to and click the "Restore" button:

Restoration using MineBack Ultimate

Thats all there is to it. Backups made simple.

Where does the MineCraft game client store its files?

Quick Answer :
In the folder
<World Name>
Easy Solution :
Use MineBack automatic backup solution

On Microsoft Windows, MineCraft stores its settings in the users "Application Data" store. The specific location of this store varies by configuration so the best way I find to access the folder is to first open the Documents folder:
Documents Folder

Next, click on the address bar (where circled) to enable text entry, and type : %appdata%\.minecraft

Address Bar, enter %appdata%\.minecraft
Under this folder there are several sub-folders each for an aspect of the MineCraft game:
Contains the core game binary Java code compressed into ZIP formatted JAR files.

There is typically 4 JAR files:

minecraft.jar(3,772 KB)Main Game Code
jinput.jar(223 KB)Java Utility Support for Direct Input
lwjgl.jar(722 KB)Lightweight Java Game Library (LWJGL)
lwjgl_util.jar(136 KB)Lightweight Java Game Library Utility.
native DIR Contains Microsoft Windows format dll's to support Open GL and direct input.
md5s (1 KB) MD5 Checksum value which may be used to validate that MineCraft is unchanged / unmodified.
version (1 KB) Version Number.   1326382442000
Contains game resource, particularly sound effects (e.g. Ambient [Weather, Cave Sound Effects], damage, fire, liquid, mobs [blaze, endermen, gast, chicken, cow, creeper])
Contains folders named with the same name as the world when it was first created (if the world is renamed the folder does not change).

See Anatomy of a World.
Whenever F2 is pressed in game a screenshot is taken and placed into this folder saved in Portable Network Graphic format (PNG).

The files are named in the following syntax :

This folder appears to contain files to be submitted to the server containing play details (?)
MineCraft will look in this folder for alternative skins for the game and its user interface. The graphics which compose the texture pack are stored in ZIP format files with an hierarchical structure. See how to create a texture pack.

What data is stored in a MineCraft save folder?

Quick Answer :
The save folder contains, Map Data (data), World Data (region), Nether Data (DIM-1), Level Data (Level.dat), Session Data (Session.lock)

MineCraft creates the following files under the save folder (not all files are required, but level.dat is critical):
level.dat(<1 KB)Level Data (e.g. Inventory, Weather, Experience, Health etc)
level.dat_old(<1 KB)Backup of Level Data (used when file corruption is detected).
session.lock(<1 KB)Use unknown, though likely a file lock and/or user identification mechanism.
MineCraft creates the following sub-folders under the save (not all folders are required):
Contains files holding the data shown on your in game maps.
idcounts.dat(12 Bytes)File for keeping track of number of Maps created.
(<1 KB) Map number
 stored in NBT format.

Note: All Maps are stored here regardless of dimension for which they where created in (e.g. Nether, World or End).
Sub-folder containing the data related to the End world (aka The End). This folder typically contains only a single sub-folder named 'region' which contains region files which store the End world blocks.
Sub-folder containing the data related to the Nether World aka Dim(ension)-1. This folder typically contains only a single sub-folder named 'region' which contains region files which store the Nether world blocks.
Contains MCRegion files are named in the following syntax :

r. y . z .mcr

Where y and z are region coordinates.

How do I create a Texture pack for MineCraft?

Quick Answer :
Extract the following folders from the minecraft.jar ZIP format file (achievement, armor, art, environment, gui, item, misc, mob, terrain). Extract the following files from the same source (pack.png, pack.txt, particles.png, terrain.png). Using a suitable image editor, customise the PNG format graphic files. Change the text in the pack.txt to be the name of your texture pack. Using a file ZIP'ing program, compress all the files and folders in the same locations as extracted. Copy the resulting ZIP file into the 'texturepacks' folder where MineCraft store its data.

MineCraft uses the following files under from MineCraft.jar or from the texturepack ZIP file selected in game to render the world graphics:
pack.png(26.6 KB)Portable Network Graphic (PNG) format Picture representing the Texturepack (shown in the Texturpack selection menu)
pack.txt(<1 KB)Name of the Texture Pack (used in the Texturpack selection menu).
particles.png844 BytesPortable Network Graphics (PNG) format file (contains: Smoke, Splashes, Drips, Bubbles and Hooks).
terrain.png55.4 KBPortable Network Graphics (PNG) format file (contains block face graphics)

MineCraft uses the following sub-folders under the MineCraft.jar or from the texturepack ZIP file (not all folders are required):
Contains player skins used for each type of armor (e.g Cloth, Chainmail, Iron, Gold and Diamon).
(964 Bytes)Upper Body (e.g. Head, Chest and Arms) art for armor of the specified material type.
(523 Bytes)Lower Body (e.g. Legs and Feet) art for armor of the specified material type.
Contains a single Portable Network Graphics (PNG) format file. kz.png containing the graphics for all the paintings which can be placed.
Sub-folder containing the graphics for rendering the weather:
clouds.png(20.2 KB)Pre-generated map of cloud cover.
rain.png(2.49 KB)Graphic used to render the rainfall.
snow.png(818 bytes)Graphic used to render falling snow.

More to come.