All sub doamins belong to you.
To make your domain name public you need to do the following steps --
1. At your registrar, designate at least one name server. For example. If you register your domain at godaddy.com, you need to either use their name server or enter your own name server. This means that if someone want to connect to www.abc.com, the top domain servers (.com, .cn, .net) can direct the request to the proper name server. say you entered 213.111.111.111 as the name server. The name server MUST have a static IP.
2. In the name server, say 213.111.111.111, you have to have an "A" record for every sub name.
Good luck