Issue regarding Rigidbody2D

I have been running via an online walkthrough to learn the basics of creating a basic 2D game via Unity. However, since this walkthrough had been written a while ago I have been having issues regarding the code. Can anyone help me out?

using UnityEngine;

public class Player : MonoBehaviour
{
	public Vector2 speed = new Vector2(50, 50);

	private Vector2 movement;
	
	void Update () 
	{
		float inputX = Input.GetAxis ("Horizontal");
		float inputY = Input.GetAxis ("Vertical");

		movement = new Vector2(
			speed.x * inputX,
			speed.y * inputY);
	
	}

	void FixedUpdate()
	{
		rigidbody2D.velocity = movement;
	
	}
}

As another source I have included the link to the web page I have been working from below.

@GiggyLapisar

Try this

using UnityEngine;

public class Player : MonoBehaviour
{
	public Vector2 speed = new Vector2 (50, 50);
	private Vector2 movement;
	private Rigidbody2D playerRigid;
	
	void Start ()
	{
		playerRigid = GetComponent<Rigidbody2D> ();
	}
	
	void Update ()
	{
		float inputX = Input.GetAxis ("Horizontal");
		float inputY = Input.GetAxis ("Vertical");
		
		movement = new Vector2 (
			             speed.x * inputX,
			speed.y * inputY);
		
	}
	
	void FixedUpdate ()
	{
		playerRigid.velocity = movement;
		
	}
}

The code is untested but should work for you