On Linux, two files need to be modified to allow connections other than from localhost:
postgresql.conf, change the listen_addresses = "*" to accept connections from anywhere. Then add a line to the pg_hba.conf file to allow access to the database from a particular IP or network. If you are not worried about security, entering:
host all all 192.168.1.0/24 trust
will allow anyone on the 192.168.1.0/24 network access to any database. Obviously this should only be used to test you can reach the database. Constrain this to the web servers IP address and use md5 so encrypted password authentication is used.