Instead of only spawning regular items, this add-on lets your spawners/generators either spawn literal XP orbs or spawn items that automatically convert into XP when picked up. Every collected orb or converted item grants players experience levels, which they can spend in the shop and upgrade shop.
You don't have to replace all of your existing spawners. Mix and match however you like - keep your current item generators, use XP orbs or XP-converting items for special events, or convert every generator into an XP source. The choice is entirely yours, making it easy to customize the gameplay to fit your server.