rigidbody.AddForce() - I just don't understand it.

Hi. I’m very new to Unity3D, and trying to code something, which lets a ball move.
My Code:
using UnityEngine;
using System.Collections;

public class ActPos : MonoBehaviour {
	private GameObject playercam;
	private GameObject player;
	private Rigidbody playerbody;
	// Use this for initialization
	void Start () {
		playercam = GameObject.Find ("playercam");
		player = GameObject.Find ("player");
		Rigidbody playerbody = player.AddComponent<Rigidbody> ();
	}
	
	// Update is called once per frame
	void Update () {
		Vector3 distance = new Vector3 (10, -2, 0);
		playercam.transform.position = player.transform.position - distance;
		if (Input.GetKey ("up")) {
			Vector3 move = new Vector3 (10, 0, 0);
			playerbody.AddForce(????);				//Heres my question
		}
	}
}

What to put into the playerbody.AddForce() to let the player move 10 on the x axis?
And did I even declare the Rigidbody the right way?
Sorry, as already mentioned, I’m new to Unity, and to C#

This is the documentation on rigidbody.AddForce:

Also, I’d recommend using GetComponent instead of AddComponent (line 9) with a rigidbody on your ball by default, but I guess it’s whatever floats your boat. This is how you could write your AddForce line:

playerbody.AddForce(transform.[DirectionYouWantYourBallToMove.  In X-Axis case it'd either be transform.left or transform.right] * speed, ForceMode.Force);

You could declare a variable speed and then make it public so you can set it in the editor. I’m assuming in this case you’ll want it set to 10. Here’s also the documentation for ForceMode if you want to read up on how that works:

Let me know if that helped!