How to open plugin editor in unreal engine 4.10 editor.
There is no “plugin editor” in unreal engine.
To make plugins requires the use of C++.
Complete instructions can be found in the official documentation:
https://wiki.unrealengine.com/An_Introduction_to_UE4_Plugins
https://docs.unrealengine.com/latest/INT/Programming/Plugins/index.html
There is also a good youtube tutorial, with source code, located at:
https://www.youtube.com/watch?v=vV0_IFD6xbc
And there is also the wiki page, with open source code plugins: