Non-exclusive means that you are not the only person with access to the item. Others will also be licensing and using the same item.
Yes. You can customize our items to fit the needs of your end product.
The item is what you purchase from Envato Market. The end product is what you build with that item.
Royalty free means you just need to pay for rights to use the item once per end product. You don't need to pay additional or ongoing fees for each person who sees or uses it.