Provided you haven't made any configuration changes to your wireless network, go look at the sticker on the bottom of the router and get the SSID and network key off of it (for better security, you really should change these and use a different security method, but it will get you up and running and you can work on the rest later).
On your laptop, do you have a little "wireless" icon in the system tray? If so open it and look for the network with the SSID which matches the value you found on the router and click "Connect". It will ask you for a key or password which is the other value you recorded from the sticker. That should do it.
If you don't have the little wireless icon, got into your control panel and look for wireless network setup. (You didn't say what OS you're using on your laptop, so YMMV here as each OS is a bit different). If you let folks here know what you see, someone will be able to post more specific instructions.
