Viewport or other Tabs In Custom Editor Window?

Wondering is its possible to add an already existing Module to a Custom editor window. Ive been searching around for hours now and cant find any info on this. been trying to get either a viewport and or a skeletal tree to show up with no luck on finding any info on how to go about doing this. Also cant seem to find any info on adding multiple Tab Lay outs to 1 window . i was planning on just customizing a skeletal mesh class but i cant seem to get the class to compile . I keep getting error lnk2001 and error lnk2019 errors when i try to create the class. if any one has any information on the custom editor windows or the errors please let me know im pretty much stuck since there is not much information on these kinds of things.