If you haven’t already check out this guide:
https://docs.unrealengine.com/latest/INT/Engine/AI/BehaviorTrees/QuickStart/
The logic for a ‘Follow AI’ or ‘Move to AI’ task would be very similar to this part:
https://docs.unrealengine.com/latest/INT/Engine/AI/BehaviorTrees/QuickStart/12/index.html
Your AI’s Blackboard may need to store a different type if your intended AI target class is different from your PlayerCharacter class. The general idea is the same though.
If you want more in depth on the basics, you might want to pick up an UE4 book like Unreal Engine 4.X by Example, from Benjamin Carnell. It has a similar tutorial to the one linked above with a little more in depth explanation.
Or check the web! There is bound to be a blog out there, going over Tasks and using Blackboards to set targets and remember other values.
The logic for a chase AI will be more complex, and as CDMc said will be highly dependent on other context in your game