The Rinnegan originally belonged to the Sage of the Six Paths. He then divided his power between his two sons, which formed the Senju and the Uchiha. For any human being to be able to activate Rinnegan, they need both the Uchiha and Senju DNA. Uchiha Madara, in the last days of his life, was able to activate it, as he already had the Eternal Mangekyo and Hashirama's cells (Senju DNA), making him similar to the Sage.
But the question is: how was Nagato able to re-activate it? Yes, it was Madara who had implanted his Rinnegan in him at a young age, but then, even though the eyes were implanted, Nagato neither had the Uchiha DNA nor the Senju DNA to be able to re-activate the Rinnegan. How was he able to do it?
And as a continuation to it, let's assume he was able to re-activate the already awakened Rinnegan (Madara awakened it originally), how was he able to use it so well and control it without his body taking a toll? He belonged to the Uzumaki clan who may have been the distant relatives of Senju, but that doesn't justify how he was able to control it so well as he did not have any trait of the SO6P, unlike Madara who could now be compared to the Sage (with both DNAs and the Rinnegan).
An example to highlight this is of Kakashi. He got a Sharingan from Obito. But since Kakashi wasn't an Uchiha, his body would take a huge toll on him whenever he used it and had to cover his Sharingan when not using to save Chakra. Though later he trained and excelled at it, he still was a non-Uchiha and thus, his body used to take the toll, though, only after excessive usage. Similarly, since Nagato has no traits of the Sage, his body shouldn't have been able to take the toll of Rinnegan activated full and controlling his 6 Pain paths, and all.
Can somebody please give a detailed explanation of how Nagato was able to awaken and control the Rinnegan?