2D character movement

You can try with this :)

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class PlayerMovement : MonoBehaviour {
 
     //[SerializeField]
     public float maxSpeed = 10f; // Maximum speed player can have
 
     //Facing of player. It can be Left or Right.
     bool facingRight = true; 
 
     // Rigidbody 2D component you need to add to Player GameObject
     private Rigidbody2D rb;
 
     private Animator animator;
 
 
     void Start ()
     {
         rb = GetComponent<Rigidbody2D>();
         animator.GetComponent<Animator>(); 
     }
     
     // It is better to do this things like movement in Fixed Update
     void FixedUpdate ()
     {
         ///<summary> You dont need if statement to check GetKeyDown(). GetAxix("Horizontal") will check if Player pressed keys (Left or Right Arrow, A or D).
         ///You can also change this in Input Settings if you want 
         ///</summary>
         ///
         float move = Input.GetAxis("Horizontal");
 
         rb.velocity = new Vector2(move * maxSpeed, rb.velocity.y);
         
         if(move > 0 && !facingRight) // Run Right
         {
             Flip();
             animator.Play("RunAnimationName");
         }
         else if (move<0 && facingRight) // Run Left
         {
             Flip();
             animator.Play("RunAnimationName");
         }
 
         else // Idle 
         {
             animator.Play("IdleAnimationName");
         }
     }
 /// <summary>
 /// This function Flip player Sprite Left or Right
 /// </summary>
     void Flip()
     {
         facingRight = !facingRight;
         Vector3 theScale = transform.localScale;
         theScale.x *= -1;
         transform.localScale = theScale;
     }
 }