I want the player to move on to the next level once it has collected a coin. What would the script for that be?

Do you have something already and need help on a specific part? If so, explain where you're stuck. If not - use google and the unity forum. On Unity answers you can ask about specific problems not requesting finished scripts :)

However you would first create a coin with a collider on it. Same goes for the player. On your player you would place something like:

 void OnCollisionEnter(Collision collision)
 {
    if(collision.gameObject.tag == "Coin")
    {
       Application.LoadLevel("nextLevelName");
    }
 }

You need to set the tag of the coin to Coin to make this work. You can also set the collider to trigger and use OnTriggerEnter

Here is the same with Javascript. Add this to the Coin and name your character as Player. Select the "is trigger" in the collider settings of the coin.

 #pragma strict
 
 function Start () {
 
 }
 
 function Update () {
 
 }
 
 function OnTriggerEnter (other : Collider)
 {
     if (other.collider.gameObject.tag == "Player")
     {
         Application.LoadLevel("TheNameOfTheNextScene");
     }
 }