Too Long; Didn't Read
Plasma Cash is a child chain consisting of a smart contract and a private Node.js-based network. It periodically commits its state to the Ethereum root chain. Plasma Cash nodes take all transactions (up to 1 million) from the pool, assemble them into a block, and calculate the Merkle Tree according to the hash. This block is sent to other nodes for verification. The root chain knows nothing about transactions generated and transferred within the child chain. It is only publicly known who added or withdrew ETH to/from Plasma Cash. A child chain allows organizing anonymous transactions using zk-SNARKs.