How to Change Skin Minecraft (Custom Skins)
A skin refers to the texture that is placed onto a player model or mob.
The skin is divided into areas that act as the surface area of the character (For example, there’s the front head area, left leg area, etc.). A skin will only allow solid color; transparency is not allowed on the skin file except on the second layer, which is transparent by default; playing offline, pixels can be left free resulting in “holes” in the skin. The second layer can be used to give the character glasses, hats, or other accessories (even a bigger head).
A skin can also refer to other textures in the game, such as block textures, item sprites, mob skins etc. A list of these can be found here.
It is worth noting that Pigmen, Zombie, and Zombie Pigmen mobs can use typical player skins (and vice-versa). Skeleton mobs can use typical player skins as well, but keep in mind that they have their skinny arms and legs. (If a skeleton mob skin is used as a player’s skin, their legs and arms will not be skinny.)
Creating a skin
Many players want to have a new look, something which describes them. While you can always search the internet for a previously made skin, many players prefer to create their own.
A custom skin is a great way to personalize your player model and can be done either by using a variety of community-made skin editors, or by editing the “steve.png” file manually with an image editor like Photoshop, GIMP, Paint.net or similar image editors. The “steve.png” file can be downloaded from here. When editing the “steve.png” file manually, be sure to keep the original image dimensions and make the background of the skin (the unused pixels) completely transparent. Otherwise, Minecraft may fail to recognize the skin as intended.