check replication slots postgres - New in postgres 10 victory 888 slot

Streaming Replication (SR) is a way of achieving High Availability with Postgres. There are many parameter settings that need to be set correctly for streaming replication.

An introduction to logical replication and change data capture ... Logical replication is a method of replication where Postgres uses the WAL files and transmit those changes to another Postgres database, or a system that supports reading WAL files.

Postgres replication is a powerful tool for replicating data between databases; unlike physical replication, logical replication gives you more control and flexibility over what data is replicated and how it's used.

Can someone suggest the steps to check pgsql replication status and how to identify if the replication is not happening properly? We use streaming replication with pgsql9.0 and pgsql9.4.