CS0120 OBJECT REQUIRED

Based on your photo @FortisVenaliter is entirely correct and his answer should be accepted as such. You are attempting to access an instance member variable (velocity) but you are trying to access it via a type "RigidBody2D" which you cannot do. You can tell its being read as a type ins$$anonymous$$d of an instance since it is coloured as such in your code. You need to get an instance of a rigidbody2D in order to be able to access the non-static variables.

The two links provided by Fortis provide all the information you would need, but if you are struggling, feel free to paste the entire script and I'll show you what to change.

Ok so the issue here is that this script is likely from an older version of unity, in which rigidbody2D (notice the lowercase r not uppercase R) was a property that you could access on a monobehaviour. This is no longer the case as such properties have been deprecated and should be avoided. I've updated this script to store a reference or type RigidBody2D which is then set using a GetComponent in the Start method. the rest of the code then utilises this variable.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class RobotController : $$anonymous$$onoBehaviour
 {
     //This will be our maximum speed as we will always be multiplying by 1
     public float maxSpeed = 2f;
     //a boolean value to represent whether we are facing left or not
     bool facingLeft = true;
     //a value to represent our Animator
     Animator anim;
 
     // This will hold the reference to our rigidbody2d component.
     private Rigidbody2D myRigidBody;
 
 
     // Use this for initialization
     void Start()
     {
         //set anim to our animator
         anim = GetComponent<Animator>();
         // get the rigid body component.
         myRigidBody = GetComponent<Rigidbody2D>();
     }
 
     // Update is called once per frame
     void FixedUpdate()
     {
 
         float move = Input.GetAxis("Horizontal");//Gives us of one if we are moving via the arrow keys
                                                  //move our Players rigidbody
         myRigidBody.velocity = new Vector3(move * maxSpeed, myRigidBody.velocity.y);
         //set our speed
         anim.SetFloat("Speed", $$anonymous$$athf.Abs(move));
         //if we are moving left but not facing left flip, and vice versa
         if (move < 0 && !facingLeft)
         {
 
             Flip();
         }
         else if (move > 0 && facingLeft)
         {
             Flip();
         }
     }
 
     //flip if needed
     void Flip()
     {
         facingLeft = !facingLeft;
         Vector3 theScale = transform.localScale;
         theScale.x *= -1;
         transform.localScale = theScale;
     }
 }

Does the object that this script is placed on have a RigidBody2D component on it? If not then that would account for some runtime null ref errors. I assumed the tutorial had already had you put that on the object, What are the errors you are getting now, are they compile errors or runtime?