I don't know the technical description but in short the normal direction affects the way poly's attach and/or interact with each other.
If you attach 2 poly's with different normal directions you get something i describe as funky stuff

After you made sure the normals are pointing the correct way (see image)you"ll have to combine the two spheres then you can connect them by using the append to polygon tool select adjacent edges and connect them then press Y to repeat the last command and go to the next pair of edges