DI-624 router, nice, I had one of those for years it was very reliable. There are different versions of the DI-624, yours may be slightly different than my instructions, if you do not have WPA2 or WPA-PSK use WEP
Here are the instructions.
In a web browser, go to the router’s settings page. (it should be http://192.168.0.1/ )
Login in
User name = admin
password is blank, there is no password (by default, if somebody added one and you do not know it you need to reset the router to factory settings, see manual)
Click on Wireless on the left side menu
Choose an SSID (name for your network, it can be whatever you like)
Write down the SSID, you will need it for any computers connecting wirelessly to your router.
Choose Authentication: WPA2 or WPA-PSK or WEP (WPA2 is best, WPA-PSK is good, WEP is just OK)
Make up a passphrase (Make up anything, 8 to 63 characters)
Write down the passphrase, you will need it for any computers connecting wirelessly to your router.
Enter the Passphrase
Click Apply
Your router will restart
Done