Board Thread:Naruto Discussions/@comment-46214474-20200629021640/@comment-32685487-20200629161611

In Madara's case BZ could have easily shown him everything through their mental connection, or what is most likely is that Madara knew the techs and how the techs worked from when he was actually alive, so I think what really happened is he practiced using his Rinnegan and the techs that come with it before he transplanted his eyes into Nagato, it was never said that he immediately transplanted his eyes into Nagato once he awakened Rinnegan.