I can also access via the default gateway address.
Does this mean you can access it from the gateway's internal address (from whatever is acting as your gateway - usually a router) or from out on the internet using the gateway's external IP address ?
Giving it a domain name usually involves either buying a domain, or using one of the ones provided by Dynamic DNS services. What have you done so far ?.
Its exactly the same process as setting up any other internal server type device although it doesn't come with setup software from the manufacturer like many NAS and IP cameras do