what is in duoling plus? is this more advanced?
It just removes the Ad when you open Duolingo to study different languages and you must pay some money for it per months by credit card
It's a way for you to support Duolingo if you so choose. It doesn't offer any more content, but it does remove all ads from both the app and the website.
Also, if you need more advanced content, Duolingo said they would soon release the skill levels update. This will allow you to access more advanced content in each topic.
You can read more about it, in their post, here: https://www.duolingo.com/comment/25615588/Upcoming-Feature-Skill-Levels