You can use the josql SQL command utility to connect to network by using:
josql <network> <user> -h <host>
<network> is the name of the network you want to connect to
<username> is the username you wish to connect as
<host> is the host address of a catalog server.
If you are using another query client or BI tool then use a standard PostgreSQL driver; and a connection string with a catalog host address and the network name for the database.