DNS is not really something we can help you with.
On the most simple level though, we can try to explain a bit. Your Atlassian server(s) have IP addresses, which is the raw unique place to get to them over a network. In a lot of cases, these IP addresses will be local to your network only, and if you want to get to them over the internet, you will be using NAT and a proxy.
As an example of this, my house has around 50 things hooked up to a network. Lightbulbs, a home hub, media players and streamers, dev servers, security devices, test servers, a printer, our mobile 'phones, my laptops and her iPad, and and and. All of these devices have an ip address of 192.168.0.<something>. They are all eventually connected to a router that is connected to my Internet Service Provider. The router is 192.168.0.1 internally, and to the internet, it appears as one unique IP address that my ISP allocates. Because I use proxies and port forwarding, a browser can go to <my ip address>/jira and see my Jira system.
A DNS service is a lookup of a human address. It's far easier to explain this with a simple analogy - your family and friends (probably) all have 'phones. Their number is the IP address, but their name is what you look for. DNS is the address book.
So. If you put your Atlassian services on the internet, you will be able to get to them via your public IP address. If you want a name for them, which resolves to the IP, you will need to buy the domain name for it, and get that name set to go to your IP. (Although that's the same service really, even the cheapest minimal option is "here is your domain url, what IP should it go to?")
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.