Replication level in FS

Good day! I have a question regarding the usage of the replication level when publishing a file: what exactly does "the service pushes blocks (for the file) to other peers" mean? Does it create copies of the blocks generated for the file and sends them to the other peers?

NSE service PoW

Good evening, is it recommended to connect to the NSE service if I want to mitigate a Sybil type attack?