Beginner question about GetComponent

Okay, I tried desperately searching the Q&As and rewatched the tutorial multiple times and I just cannot wrap my head around this “simple” function. I have a variable called “diceroll” in a script called “DiceRoller” on a GameObject called “DiceManager”.

public class Card_AttackMod : MonoBehaviour {

GameObject diceManager;
??? diceRoller;
string diceroll;

// Use this for initialization
void Start () {
	diceManager = GameObject.Find("DiceManager");
	diceRoller = diceManager.GetComponent<DiceRoller> ();
}

// Update is called once per frame
void Update () 
{
	if (Input.GetButtonDown ("Fire2")) 
	{
		ModifyDiceRoll ();
	}
}

void ModifyDiceRoll()
{
	diceroll = Diceroller.diceroll;
	Debug.Log ("Card is accessing DiceRoller Data: " + diceroll);
}

}

I’m pretty sure my problem is in the declarations at the start of the script (hence the ???) because I can’t figure out what it wants me to declare the script as and the manual has been no help at all. Is this all I need or is there something even more that I’m not understanding about GetComponent?

diceRoller = diceManager.GetComponent ();

It tells me diceRoller is a DiceRoller (with DiceRoller being a class inheriting from MonoBehaviour) so just declare it:

 DiceRoller diceRoller;