How to create a mission system?

I want to create a mission system in ue4.But I can’t find any documentation or answer, how can I do it?
Use multiple-thread?

This is such a general question that it is hard to come back with a simple answer. There is so many ways you could implement a mission or quest system for your game depending on your needs. I recommend watching this video from the Unreal Engine Live Training. It might give you ideas on how to approach this matter.

Thank your, this video is very useful.