Access the current gamepad:

Gamepad.current

Buttons:

Gamepad.current.buttonSouth
Gamepad.current.buttonNorth
Gamepad.current.buttonEast
Gamepad.current.buttonWest

Sticks:

Vector2 move = Gamepad.current.leftStick.ReadValue();
Vector2 look = Gamepad.current.rightStick.ReadValue();

Triggers:

float left = Gamepad.current.leftTrigger.ReadValue();
float right = Gamepad.current.rightTrigger.ReadValue();

Rumble:

Gamepad.current.SetMotorSpeeds(0.5f, 1f);