How to Apply Animation to Player

Hey guys so Im making my first app. I know this is a pretty loaded question but Im having a hard time following examples because the script code is different. I am making a 2D platform runner. To start, I created the platforms, environment as well as a majority if not all of the physics. The player at this point is just a circle (just a place holder). The circle can move from left to right and jump. I have now, created an actual player sprite and made animations for walking, jumping and idle. How do I apply the new sprite animations to the current circle placeholder as well as the script? My next step is to go into the animator and start making transitions i guess. Im just not sure how to add the animations to my current script. I knew this was going to be a challenge and if there is any other info you need, please let me know. Thanks so much guys.

This is my "Controls.cs" that is currently attached to my circle player/placeholder. My CheckGround is attached to him. Everything else should be in relation to the platforms he is jumping on and I dont think will change. Again, I have a sprite walking, jumping and idle that I would like to take place of the current circle/placeholder. I need the walking animation to take place when the left and right arrows are pressed, the pump animation to play when the jump button is pressed and idle animation to play when the player is just standing still otherwise. Again, thanks so much guys!

 using UnityEngine;
 using System.Collections;
 
 
 public class Controls : MonoBehaviour
 {
     public Rigidbody2D rb;
     public float movespeed;
     public float jumpheight;
     public bool moveright;
     public bool moveleft;
     public bool jump;
     public Transform groundCheck;
     public float groundCheckRadius;
     public LayerMask whatIsGround;
     private bool onGround;
 
     // Use this for initialization
     void Start()
     {
         rb = GetComponent<Rigidbody2D>();
 
     }
 
     void FixedUpdate()
     {
         onGround = Physics2D.OverlapCircle(groundCheck.position, groundCheckRadius, whatIsGround);
     }
 
     // Update is called once per frame
     void Update()
     {
 
 
 
         if (Input.GetKey(KeyCode.LeftArrow))
         {
             rb.velocity = new Vector2(-movespeed, rb.velocity.y);
 
         }
         if (Input.GetKey(KeyCode.RightArrow))
         {
             rb.velocity = new Vector2(movespeed, rb.velocity.y);
 
         }
 
         if (Input.GetKey(KeyCode.Space))
         {
             if (onGround)
             {
                 rb.velocity = new Vector2(rb.velocity.x, jumpheight);
             }
         }
 
         if (jump)
         {
             if (onGround)
             {
                 rb.velocity = new Vector2(rb.velocity.x, jumpheight);
             }
             jump = false;
         }
 
         if (moveright)
         {
             rb.velocity = new Vector2(movespeed, rb.velocity.y);
         }
         if (moveleft)
         {
             rb.velocity = new Vector2(-movespeed, rb.velocity.y);
         }
 
     }
 
 }