i am pretty sure that this is right but.....

Pro tip: when Unity gives you an error message, Unity is correct and you are wrong.

You really need to be able to debug and solve syntax errors yourself if you want to learn game development properly. Otherwise, you will get stuck a lot. The errors here are very obvious (besides MoveTowards speed). You should also be posting the full error message and explaining the steps you have taken to solve it yourself. Most of these errors have been answered many, many time before, if you do a quick search beforehand. And do try to format your code properly. Anyway:

 using UnityEngine;
 using System.Collections;
 
 public class Skellyattack : MonoBehaviour
 {
     public GameObject player;
     public GameObject skelly;
     public float distance;
     public float speed;
 
     // Use this for initialization
     void Start()
     {
 
     }

     // Update is called once per frame
     void Update()
     {
         player = GameObject.Find("Player");
         skelly = GameObject.Find("skeleton");
         distance = Vector3.Distance(player.transform.position, skelly.transform.position);
         if (distance <= 3)
         {
             skelly.animation.CrossFadeQueued("run", 0.3f, QueueMode.PlayNow);
         }
         else if (distance < 15 && distance > 5.0f)
         {
             skelly.animation.CrossFadeQueued("attack", 0.3f, QueueMode.PlayNow);
             skelly.animation.CrossFade("run");
             skelly.transform.LookAt(player.transform.position);
             skelly.transform.position = Vector3.MoveTowards(skelly.transform.position, player.transform.position, speed);
         }
         else
         {
             skelly.animation.CrossFadeQueued("run", 0.3f, QueueMode.PlayNow);
             skelly.animation.CrossFade("idle");
         }
     }
 }