Yeah, those papers are very dense. You might want try reading zerocoin[0] first, it was the starting point of all the zero-knowledge proofs for private payments on a blockchain. Then another academic paper, Pinocchio coin, had a proposal for zkSNARKs. And Zeorcash built the zksnark + merkle tree+ serial umber (later called a nullifiers ) approach.

[0] https://www.cs.umd.edu/~imiers/pdf/ZerocoinOakland.pdf