Okay so I have my aunts old Dell Latitude D600 and I have a wifi set up at my house but I'm not sure how to get my laptop to c

On your laptop:

make sure the wireless adapter is enabled.
Then, go to "Control Panel >> Network & Sharing Centre".
In lower half of large panel, click "Connect to a network"

A panel should pop up showing the list of available networks.
Click the network name that applies to you (ie your router's ID name or SSID).
Enter your router's wireless key in the box that appears.
Click 'OK'