How to setup a sub domain?

[ByteChanger]

I'm not sure if I'm using the correct terminology. I'd like to try out this software.

I have a static IP, but do not have a registered domain name. Basically, I signed up at DynaDNS and they gave me a subdomain. (or maybe a sub-sub domain?)
getmyip.com

So, if I type myname.getmyip.com into any browser, they are directed to my IP address. Works good for that.

Can I use user1.myname.getmyip.com? Will this program let me do that? That is basically my main question.

or do I have to have my own registered domain name? ie: http://www.name.com

Thanks for the help, looks like a really handy program.