Thanks fro the info - I am new to Odoo , could you tell me step by step with code of doing this please.  Really appreciate it and sorry for asking basic questions. 

An Odoo instance can have multiple databases, see .../web/database/selector URL to see all your databases. On a server you can also install multiple Odoo instances using different ports (8069, etc.). As long as you do not use OCA's multi-website module, you can assign one hostname (subdomain.domain.tld) to one database.

You have 2 options to link hostnames to databases:

1. dbfilter configuration parameter in odoo.conf file
Depending on your regex expression you can assign subdomains or hostnames to database names

2. OCA module dbfilter_from_header
Allows you to directly assign a database name to a http request header in your proxy server vhost definition.