DNS is "Domain Name Server."  That's separate from DDNS (though somewhat related).

DNS servers are what translate Domain Names (like CNN.com, or NakedMILFSinLeather.com) to IP addresses.  Without them, you'd have to know the IP address to every website you want to visit... but thanks to DNS, you can enter something that makes sense to a human being, and the DNS server will take the request, translate it into the appropriate IP address, and send that back to your computer.  Without that DNS server, or the actual IP address, you couldn't get anywhere on the internet.  Your ISP (cox, roadrunner, time-warner, AT&T, etc) may have their own DNS servers to speed things up... but you can always use Google's public DNS servers.  They are:

8.8.8.8
8.8.4.4

That is DNS.

DDNS is something a little different.  It stands for Dynamic Domain Name Server.  This is for people on cable modems, DSL, etc where they are dynamically assigned an IP address by their internet provider, and that address periodically changes.  Most residential internet services use DHCP to assign IP addresses (Dynamic Host Configuration Protocol) to your cable modem.  Whenever you power-cycle your modem, it logs onto the cable/DSL provider's network, asks for an IP address, and the DHCP server assigns one.  It's often a different one every time, and can change every few weeks.  As you might imagine, this would be catastrophic for a commercial website, because if they didn't update the DNS servers with their new IP address, nobody would know where to find their webpage; the web traffic would keep getting routed to the old IP address.

This is also a problem when you have cameras that you want to access from another location.  If you don't know the IP address (or even if you do, but it just changed), you can't reach any of your stuff.  This is a common problem, and thus arose various Dynamic DNS services.  These services usually give you a "domain name" of some sort (bigARshooter.webhop.net, or something similar).  The service assigns your IP address to that domain name, and whenever you want to access your stuff, you just enter that domain into the browser, followed by whatever port number you forwarded through your firewall to the DVR/NVR.  So it would be http://bigARshooter.webhop.net:8888, or whatever port you chose when you set up the firewall.  

There are little client programs that run on your network/router, and keep track of your external IP address.  Whenever it changes, they automatically update your DDNS provider's server with the new IP address.  This keeps "BigARshooter.webhop.net" assigned to the correct IP address.

Does all of that make sense?  Let me know before we move on.

The only potential complication I can anticipate is that you're on a WISP (wireless Internet Service Provider).

If they're firewalled somewhere upstream, you'll also need to change THOSE firewall settings to get internet traffic through to your IP address (and hopefully you have a Static IP from your WISP).

Might not be a big deal, if you have a routable IP address, and they're not filtering/firewalling upstream.

What is the IP address of your computer (on the LAN... eg. on the inner side of the router)?  Type "ipconfig" at a DOS prompt if you don't know how to check.  It should give you a 192.168.x.x type of IP address.

Ignore the certificate errors.  That should be the webpage into the router... it's just throwing those because it's trying to setup an HTTPS connection, and doesn't recognize the cert.