1) The Wii U Pro controller is a controller for the Nintendo Wii U that is suited more for players who prefer the classic control scheme instead of the Wii U GamePad, with its tablet screen and more.
2) The Wii U Pro controller is standard sized and resembles a lot to the Xbox 360 controller in its button layouts. Here is the full button layout for the controller:
a: Dual analog sticks (clickable)
b: AB and XY buttons
c: A D-pad under the left analog stick
d: A power button for the console, and a Home, select and start button in the center.
e: Shoulder bumper buttons, and dual trigger buttons as well.
f: Built-in rumble feature
g: Built-in rechargeable battery thats charged via a USB cable connected to the console.
h: Up to 4 Wii U Pro controllers can be used at the same time
3) The Wii U Pro controller is wireless and will have around 30ft (10 M) of range. Players will be able to use the controller in the majority of games instead of using the GamePad, although this would negate the advantages that the tablet screen brings to gaming.