Zero-Knowledge Proofs or ZKP for short is an important of the blockchain is a method for authenticity with no passwords shared these means that is impossible to steal the information this protects the transaction and the data of everyone this protocol doesn't share the information with the network 

This ZKP allows a way of posting private transactions on the chain while maintaining privacy in this case for the transaction the common token that has been in use is Z-cash the addition of this technology in the blockchain helps to send important things important transaction encrypting the that in different chunks letting users to some people to see while other people can't  

Zero-Knowledge Proofs leads us to Zero-Knowledge Rollups Vitalik Buterin has talked about these protocols this layer 2 allows the blockchain to make a faster validation with minimal fees these have many things to improve many ways to improve it some tokes that run under this protocol are IMX these is aiming to be an NFT market with minimum transaction fees and no mitinig this zero knowledge can mint faster than layer 1 Zk-rollups are becoming very popular with developers and investors also traders because the low fees and the future that they have some ZK rollups projects are

Zk Sync  https://zksync.io/ 

Loopring (LRC)  https://loopring.org/#/

Syscoin (SYS) https://syscoin.org/ 

Immutable X (IMX) https://www.immutable.com/ 

Remember do your investigation this is not an financial advise 

Talking about layers the number 1 is a base layer that improves the base protocol that help the coin.

Layers 1 blockchains include Bitcoin, Ethereum, Binance Smart Chain (BSC) Litecoin and Avalanche

Layer 2 is a network over layer 1 those run by smart contract these protocols create the ecosystem