Leveling system

Thats a broad question. Perhaps it would help others provide an answer if you can describe where you have difficulties.

Well here is a basic example of a progress bar with an exp amount, a maxExp amount. This test lets you add exp by pressing the '+' on the keypad. In this example, I have exp starting at zero, maxExp set to 1000, and a Texture that fills in the background (gui box) as you progress. No matter what you set your maxExp to, it will never overfill the background box, since the simple formula here keeps the fill based on the percentage of the width of the box. I've attached an example of what kind of texture you could use, just a 32x32 green fill. Assign this texture in the inspector. The higher you set your maxExp, the slower this will fill.

 using UnityEngine;
 using System.Collections;
 
 public class Example : $$anonymous$$onoBehaviour
 {
     public Texture2D bar;
     Rect bgRect;
     Rect barRect;
     Rect labelRect;
     int exp = 0;
     public int maxExp = 1000;
     
     void Awake()
     {
         bgRect = new Rect(32, 32, 512, 24);
         barRect = new Rect(34, 34, 0, 20);
         labelRect = new Rect(32, 64, 128, 24);
     }    
     
     void Update()
     {
         if(exp > 0)
             barRect.width = exp * bgRect.width / maxExp;
         
         //TEST
         if(exp < maxExp)
         {
             if(Input.Get$$anonymous$$ey ($$anonymous$$eyCode.$$anonymous$$eypadPlus))
                 exp += 10;
         }
     }
     void OnGUI()
     {
         GUI.Box (bgRect, GUIContent.none);    
         GUI.DrawTexture(barRect, bar);
         GUI.Label(labelRect, exp.ToString());
     }
 }