To be clear, I have never had a zone level service from DYN but I do have host services. But it sounds like you have already figured out the zone part. So for hostnames, all you do is add a new hostname (i.e. yourcustomer.yourcompanyname.net), then enter that hostname, your Dyn username, and Dyn password into whatever device you want to host DynDNS.

For example, we usually do the router, but you could also do it with a camera, DVR, or other network device that supports DynDNS. The router (or other network device) will then tell DynDNS whenever the WAN IP changes, so that the yourcustomer.yourcompanyname.net URL will direct to the correct IP.