Monero and Zcash are both privacy-focused cryptocurrencies, but they use different technologies to achieve privacy.
Monero uses a technology called "Ring Signatures" and "Stealth Addresses" to obfuscate the sender, receiver, and transaction amount in each transaction. This makes it difficult to trace the transaction details.
Zcash, on the other hand, uses a technology called "zk-SNARKs" (Zero-Knowledge Succinct Non-Interactive Argument of Knowledge) which allows for completely shielded transactions where all transaction details are encrypted. Users have the option to send transparent transactions as well, where the details are visible on the blockchain.
In summary, Monero focuses on privacy through obfuscation techniques, while Zcash offers both transparent and shielded transactions using zk-SNARKs.