The Ender Chest allows the player to place items in the chest and access them from another ender chest or pouch with the same color code (the three colors located on the ender chest's top face) anywhere in minecraft (including both the overworld and the nether), effectively transporting items without the use of teleport pipes or long chains of transportation pipes. Using ender chests instead of transport/teleport pipes reduces lag dramatically and allows the player to transport items from the nether, an ability pipes do not have.
The Ender Pouch is the mobile form of an ender chest. It allows the player to carry it around, placing items into it as they go, without having to place it, as they would if it were the chest. When they die and lose their items, including the Ender Pouch itself, they can craft the Ender Pouch or Chest corresponding to the color scheme of the Ender Pouch they lost to get the items they placed in the original Ender Pouch back.