The Wii U GamePad is a tablet like controller that supports off TV play.
The Mario Kart game for the Wii U is Mario Kart 8. It can be played on the Wii U GamePad.
The GamePad does not have the ability to control Wii games, but what it does have the ability to do is display the screen. If you press + on the Wii Remote before the Wii Menu starts, it will display the GamePad only and not the TV.
The GamePad can do different things. For example it will display a different screen than the TV sometimes.
The Wii U GamePad has different parts. Some will have no description.
A - Usually games use to confirm.
B - Usually games use to cancel.
D-Pad - Can be uses if you are steering in Mario Kart 8.
Left Joystick - The joystick on the left side. Pushing force on it will make a "click" sound.
Right Joystick - The joystick on the right side. Pushing force on it will make a "click" sound.
+ (Start) - Games usually use to pause the game.
Power - Turn on/turn off the power.
TV Control - Set up TV Remote in System Settings.
Battery Power - If the circle does nothing, it's fine. If the circle is orange, the Wii U GamePad is charging. If the circle is red, the Wii U GamePad is almost dead. If the circle is red and flashing, it only has a few seconds to run out of battery power.
Mic - Located next to the home button.
Home Menu - Opens up the Home Menu.