The Structure Block can be used for copying structures in your world and
then pasting them somewhere else. It's a new type of block which
according according to the Minecraft wiki is an existing feature in
Minecraft Pocket Edition but can't yet (officially) be obtained.
However, if you install this add-on you will be able to access
the block and use it in-game.
Creator: ModelPart, Twitter Account
How does it work?
To demonstrate this feature I am going to show you how to copy a
structure and then paste it somewhere else.
I've added one video tutorial by RageElixir and another by EckoSoldier to the
bottom of the post.
Place down a structure block at the lower bottom corner of the structure which
you want to copy. Tap on the block and select Corner Mode and
enter a name for it, e.g. "House1". Then press Accept.
Find the opposite top corner of the structure and place down a second
structure block. Press on the block, select Corner Mode
and make sure to the same name which you used before, e.g. "House1". Then
press Accept.
Next, place down a third structure block and then tap on it once.
Select Save Mode, name it "House1", press the Detect
button and then hit Save.
Go to the area where you want the structured pasted and place down another
structure block. Tap on the block and select Load Mode. Enter
the name for the structure "House1" and then press load.
Before it actually spawns it will show an outline of the structure. This is
useful in case you want to make any changes to the position of the
structure. If it's all good then tap on the structure block again and
press Load.
I'm sure it can be used for many other things but this will give you an idea
of what you can do with it in-game.
Check out the Minecraft wiki for more information about
the block. Keep in mind that this is a BlockLauncher addon and that it might
not include all of the features which the official feature includes.