(Sorry for my bad english but I am german) I want to create a AI that follows me when it sees me (OnSeePawn). Can you give me blueprint Screenshots or Tutorials?
Hello Kay Jersch,
This tutorial should be able to help you out.
https://docs.unrealengine.com/latest/INT/Engine/AI/BehaviorTrees/QuickStart/
Please let me know if you encounter any problems trying to follow the tutorial or if it is not what you’re looking for.
Search for Peter L. Newton on youtube , you will have plenty A.I. concepts from him 
Its not working. The behaviour Tree don’t does anything
You’ll need to be more detailed than that. What part of the tutorial are you on and are you checking the Behavior Tree at runtime to see if it is getting hung up somewhere?
I made the full behaiviour tree with Tasks, Services and decorators. I checked the behaiviour tree at runtime and saw that don’t even the root does anything.
Did you finish step 6? This involves setting up the AI Controller blueprint so that it uses the behavior tree that you created. Also be sure that you did the last part of step 4, which shows you how to assign the AI Controller to your character blueprint.