The router has 5 ports on the back, one is blue and connects to the modem, the other four are grey and numbered 1 to 4 you connect any of these to the PC and now reboot the modem and wait until it settles after 2 minutes.
Then go online with the PC and click this link
http://192.168.0.1/ you will then be asked for a
username which is
admin and password which you leave blank, and then click login and they will be presented with a Dlink screen on the left chose
wireless setup and then go to
manual setup at the bottom and you will be presented with the setup screen
At the top we have Wi-Fi Protected Setup also known as WCN2, remove the Enable Pin tick and then go the Wireless Network Settings section and go to the box with the SSID which by default will be dlink and change it to one of your own choice like
Osem1234.
Then click on the security options drop down and choose WPA/WPA2 wireless security enhanced, then the Network key box will appear and in here they enter a network key/password with a minimum length of 8 characters then click save settings and wait for it to finish.
You can now look for their newly named network with the other machines and connect using the network key/password.
Try it you will be surprised at how easy it is to set up.