So basicly I couldn’t find anything usefull that touched on the basics of basics. Untill i stumbled upon this: Modular Modeling and Lightmapping Overview | Blender to UE4 - YouTube
and after unpacking light map you need to switch in Unreal Engine lightmap index back to 1, because it will make its own map on channel 2 and will point to it (that is if you will not mess with the settings).
And even after that youll still get some artifacts.
Now you have two choices:
either up the resolution of lightmap in Unreal Engine,
or you can go back to that lightmap in blender, select everything in it, and while pointing your mouse over lightmap hit CTRL+P this will pack your islands, and then you set margin on that to .150 (or something like that)
And now if you drag your cube into the world it should look and behave just like the basic cube from Unreal engine while still keeping lightmap resolution at 64.
Hope this helps to the beginners 