Plug the router into the modem.
Plug the Mac in via an ethernet cable.
The router will have a default address likely 192.168.1.1 or 192.168.1.0.
Open Safari and type https://192.168.1.1 and the router should come up.
The manual will tell you the default password and username if there is one.
Once into the router you have do some setup depending on if you are using the wireless or not. What security options to use. Also you may need to setup you Mac to use DHCP which it likely already is unless you changed it.
Open Safari and type into the address bar https://192.168.1.1 This will take you to the router setup ware.
To get past the first screen type admin and admin again for the password.
Now I'm not sure where that software will take you but somewhere in there you will need to supply three pieces of information:
You may need to select manually configure to get to the place where you can enter the following information.
--> Your ip's address-https://your.isp.name
--> Your username that you have with your isp
--> You password that you have with your isp
If your having difficulty making these settings then your best talking to your ISP or D-link support as it is not nothing to do with the Mac. So assuming you are successful entering this information then: Click OK or connect whatever the affirmative button is and if all goes well the software should indicate as much.
How to Setup Dlink Router on MAC?