private readonly object myLock = new object();
private HashSet<Gamepad> myGamepads = new HashSet<Gamepad>();

private void GetGamepads()
{
    lock (myLock)
    {
        foreach (var gamepad in Gamepad.Gamepads)
        {
            // Check if the gamepad is already in myGamepads; if it isn't, add it.
            if (!myGamepads.Contains(gamepad))
            {
                myGamepads.Add(gamepad);
            }
        }
    }   
}

Gamepad gamepad = myGamepads[0];

GamepadReading reading = gamepad.GetCurrentReading();

// returns a value between 0.0 and 1.0
double leftTrigger = reading.LeftTrigger;  
double rightTrigger = reading.RightTrigger;

// returns a value between -1.0 and +1.0
double leftStickX = reading.LeftThumbstickX;
double leftStickY = reading.LeftThumbstickY;   
double rightStickX = reading.RightThumbstickX; 
double rightStickY = reading.RightThumbstickY;

if (GamepadButtons.A == (reading.Buttons & GamepadButtons.A))
{
    // button A is pressed
}