Gravity and Jumping for a Character Controller

Hey, I was trying to work out how to add jumping and I couldn't get it to work. :/

These are the vars at the top of my script:

private var moveDirection : Vector3 = Vector3.zero;
var JumpSpeed = 8.0;
var gravity = 20.0;

and this is in the function:

//Apply gravity
moveDirection.y -= gravity * Time.deltaTime;
//Jump
if(Input.GetButtonDown("Jump"))
{
    moveDirection.y = JumpSpeed;
}

Is this the right way to go about this? is there a better way? Should the player have different components?