Evoling items require experience to make them better. For example, you'll loot something that says "Evolving: Level 1/6"
https://everquest.allakhazam.com/db/item.html?item=44755 As you kill epxerience giving mobs (now green and higher cons), the weapon/item will get stronger. In the given link, you can see the newer levels of the weapon on the right side.
Edit: In order for the evolving item to get experience, it has to be equipped. Sitting in a bag in your inventory does nothing for it.
Edited, Oct 23rd 2006 at 9:43am PDT by Wayen